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Nelchinopsis kostromiensis
Nelchinopsis kostromiensis (Vozzhennikova, 1967) Wiggins, 1972; Emendation: Harding, 1996, p.353,355, as Nelchinopsis kostromiensis.
Originally Gonyaulax kostromiensis, subsequently Gonyaulacysta kostromiensis, thirdly (and now) Nelchinopsis kostromiensis.
Tax. sr. synonym of Alaskadinium wigginsii Duxbury, 1977, according to Stover and Williams, 1987.
Duxbury, 1977, retained this species in Gonyaulacysta Deflandre, 1964. Stover and Williams, 1987, retained it in Nelchinopsis.
Holotype: Vozzhennikova, 1967, pl.26, figs.1-6; Jan du Chene et al., 1986, pl.44, figs.7-8; Lentin and Vozzhennikova, 1990, text-fig.64 (lost according to Lentin and Vozzhennikova, 1990)
Lectotype: Lentin and Vozzhennikova, 1990, pl.15, figs.5-6 (designated by Lentin and Vozzhennikova, 1990)
Locus typicus: Kostromsk region, Russia
Stratum typicum: Neocomian, probably Valanginian or Early Hauterivian
Translation Vozzhennikova, 1967: Lees in Sarjeant, 1971(Ed.)
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Nelchinopsis kostromiensis (Vozzhennikova, 1967) Wiggins, 1972, emend. Harding, 1996. According to Harding (1996, p.353,355), Nelchinopsis kostromiensis has an ectophragmal but no autophragmal apical horn. Cyst is holocavate with the maximum separation of wall layers at the parasutures. Ectophragm is minutely perforate and thin. In parasutural areas, ectophragm developed into distally denticulate septa up to 3 µm high in intergonal areas and up to 7 µm at gonal junctions. On apical horn tends to form rugulate ridges. Autophragm laevigate, bearing a dense cover of cylindrical processes up to 0.5 µm in diameter, with length from 1.5 to 7 µm. Paratabulation formula: 2pr, 4', 6", 6c, 6"’, 1p, 1"”, 5s. Apical pattern Q/B, L ventral arrangement. Most likely archeopyle type is t(A)a. Paracingulum well defined, bounded by parasutural septa. Length 51-65 µm.
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Original description: Vozzhennikova, 1967, p. 85-85: Gonyaulax kostromiensis
Theka with a rounded polygonal outline. Epitheca larger than hypotheca and with broadly rounded, coloured, subconical apical horn. The theca may have short processes wich appearently represent the raised up margins to the apical plates. Transverse furrow twisted to the left, its ends seperaed from each other by a distance equivalent to 1 - 1 1/2 times the width of the furrow. The longitudinal furrow either extends to the antapex or is seperated from the antapex by the small accessory plate (npb) which is difficult to distinguish becauce of its ornamentation. Plate formula: on the epitheka 4a + 6np, on the hypotheca 6zd + 1cp, + ?npb + 1a'. The first apical plate does not quite reach the left end of the transverse furrow. The anterior equatorial plates are trapeziform, the sixth being slightly larger smaller than the others. The first posterior equatorial plate is distinguished by its smaller size. Below it lies the small accessory plate. The antapical plate is large and polygonal. The surface of the thecal envelope is densely covered with spines. The margins of the transverse furrow and the plates are fringhed with tall, hyaline, toothed processes. Large spines occur at the angles where the plates join. No pylome has been observed.
Dimensions: holotype - length 61.8 Ám, breadth 50.6 Ám, width of transverse furrow about 6 Ám, length of apical horn 14 Ám. In other specimens length 50.6 - 64.6 Ám, breadth 50.6 -- 56.2 Ám, width of transverse furrow 6 Ám, length of apical horn 8 - 14 Ám, width of toothed processes 6 - 8 Ám.
Revised diagnosis: Wiggins, 1972, p.301
Same as for the genus with the following additional remarks. The 6", 6c 7c, 1p.s., 5'''--6''', 1p, 1p.v., 1'''' tabulation is indicated by fin-like septal membranes which are finely granulose on the lateral surfaces, and sublinear (rare) to dentate or spinose at the external margins. These septal membranes commonly obscure the precise tabulation configuration and plate junctures. The individual plating junctures are suggested by elevated peaks formed at the septal membrane junctures. All plates in this tabulation sequence appear to be ornamented with closely spaced, tubular processes that are slightly flanged or bifurcate? distally, and approximately 1.5--3.0 Ám in length. The 7c cingular plate is small and generally difficult to determine. The relative positions of the longitudinal cingulum membranes appear to be variable. The relative size of the 1''' plate to the 1p plate also appears variable, as determined by their sutural trace insertion into the sulcal region. The insertion point of this trace seems to vary from about midway along the dextral side of the 1p.v. plate to the 1p.s.--1p.v. sutural trace. The relative length of the 5'''--1'''' sutural trace also appears to be quite variable. Although Vozzhennikova (1967, p. 85) indicated a 6''' plate to be present, it was rarely interpreted on the Alaskan specimens, and 5''' is the normal postcingular plate complement. The opercular sequence of plates, the 1a.cl., 5', 6a--7a, 1a.s. series, is indicated by generally faint, low, thin, and smooth ridges. One notable exception to this rule concerns the margins of the 5a plate. The longitudinal margins of this plate are commonly defined by a low, fin-like membrane that is widest at the juncture with the 5" precingular plate and narrowest at the juncture with the 4' apical plate. The maximum width of this membrane is about 1.0--1.5 microns, and decreases proportionally in the apical direction. Occasionally a partition membrane was noted which would separate this 5a plate into platelets, and these are indicated by the notation 5a1 and 5a2. When these membranes are discernible seven anterior intercalary plates can be ascertained. Otherwise, it would be difficult to interpret more than six. The opercular tabulation sequence is ornamented differently than the previous series of plates, and it is obviously two walled in construction. The inner cyst wall is coarsely ornamented with tubular processes, whereas the outer wall is relatively smooth to granulose. This tabulated outer wall forms a distinct apical horn with approximately equal dimensions of base-width and higth. The 1a.cl, apical closing plate, on this horn is unique thickened for this series. The longitudinal traces of the anterior interclaries appear to be coincident with the longitudinal traces of the precingulars except for the 5a-6a trace, but they could be slightly offset from another. Free opercula were encountered, but a few were noted in partial detachment may or not may involve the 1.a.s. plate.
Harding 1996
Nelchinopsis kostromiensis (Vozzhennikova) Wiggins, 1972, emend. nov.
1967 Gonyaulax kostromiensis Vozzhennikova, p. 85, plate 26, figs. 1-6; plate 27, figs. 1, 2. Valanginian.
1969 Gonyaulacysta kostromiensis ( Vozzhennikova)Sarjeant, p. 10.
1972 Nelchinopsis kostromiensis ( Vozzhennikova)-Wiggins, p. 299. Valanginian early Hauterivian.
1977 Gonyaulacysta kostromiensis (Vozzhennikova) Sarjeant, 1969-Duxbury, p. 37. Hauterivian.
1977 Alaskadinium wigginsii-Duxbury, p. 37.
1987 Nelchinopsis kostromiensis ( Vozzhennikova) Wiggins, 1972-Stover and Williams, p. 11.
1990 Nelchinopsis kostromiensis ( Vozzhennikova) Wiggins, 1972-Lentin and Vozzhennikova, p. 108, plate 15, figs. 5, 6 (lectotype).
Emended diagnosis
Leptodinioidean cyst consisting of an autophragm supporting a thin ectophragm on densely-packed, solid, slender processes. Nature of archaeopyle uncertain, possibly apical. Paratabulation fully developed on the ectophragm as indicated by distally denticulate septa, these denticles being pronouncedly elongated in gonal posltions.
Emended description
Shape: Ectophragmal ambitus essentially pentagonal, made angular by the development of parasutural projections at plate triplejunctions. Epicyst bell-shaped with apical plates drawn out into a broad-based, short apical horn. The horn is hollow, distally entire and measures from 9 to 14 Ám in length. The autophragmal ambitus is subspherical and no apical horn is developed on this wall layer. Cyst shows greatest width across posterior cingular suture. Slight primary dorsoventral compression. Epicyst (less apical horn) and hypocyst approximately equidimensional. Cyst is holocavate with the maximum separation of wall layers being found at the parasutures.
Phragma: Ectophragm is minutely perforate and c. 0.2 Ám thick. This appears to consist of partially fused sporopollenin globules (Plate II, 3); in less well preserved specimens the perforations in the layer range from subcircular holes to more sinuous fissures up to several tenths of a Ám long (Plate II, 3, 6). In parasutural areas the ectophragm is developed into distally denticulate septa. The septa are up to 3 Ám in height in intergonal areas, but may attain 7 Ám at gonal triple junctions (Plate I, 1, 4, 7-9; Plate II, 1, 4, 7). The parasutural septa are much reduced on the apical horn, being represented by rugulate ridges usually lacking denticles. Associated with this, the horn is often compressed or collapsed and it can therefore be more difficult to discern paratabulation in the apical region (V. Wiggins, pers. commun.).
The autophragm is laevigate, of sub-micron thickness, and bears a dense cover of cylindrical processes (up to 0.5 Ám in diameter; Plate II, 3). The length of the processes varies from c. 1.5 Ám in intratabular areas up to c. 7 Ám in the case of processes supporting the gonal projections of the parasutural septa. Slight proximal and distal flaring of the processes is observed (Plate II, 3). The junction between individual processes and the ectophragm is not consistently marked on the external cyst surface, although in some cases a small subcircular depression is formed on the exterior of the ectophragm.
Paratabulation: Expressed in the form of denticulate parasutural septa and rugulate ridges (the latter restricted to the apical horn). L-type sexiform gonyaulacoid. Paratabulation formula: 2pr, 4', 6", 6c, 6"', lp, 1"", 5s. Apical pattern is of the Q/B type (Plate II, 2, 7), whereas the ventral region shows the lu/li arrangement (Plate II, 2). The Y/5 suture is clearly longer than the Y/3 suture, indicating an asymmetrical quadrate arrangement of the antapical region. This is an Ornatum-type paratabulation (Helenes, 1986).
Archaeopyle: A clear excystment structure has not been recognised on any of the specimens examined. The available evidence (see below) indicates that the most likely archaeopyle type is (tA)a.
Paracingulum: Well defined, bounded by denticulate parasutural septa of equal height. Laevorotatory, displaced by 1.5-2 cingulum widths.
Parasulcus: L-type arrangement with a narrow, elongate anterior sulcal, prominent flagellar scar and a large, almost circular posterior sulcal (Z) (Plate II, 4, 5).
Dimensions
Russian specimens. Measurements from Lentin and Vozzhennikova (1990). Holotype (lost): length, 62 Ám; width, 51 Ám; apical horn, 14 Ám long. Lectotype: length, 58 Ám; width, 52 Ám. Five remaining specimens: length, 51-65 Ám; width, 51-56 Ám; apical horn, 8-14 Ám long; parasutural septa, 6-8 Ám high.
Alaskan specimens. Range of 50 measured specimens from Wiggins (1972, p. 302): length, (50) 59 (70) Ám; width, (40) 51 (61) Ám, length apical horn, (8) 12 (16) Ám. These measurements are confirmed by new measurements of topotype material provided by Wiggins.
Hunstanton specimens. Length, (57) 59.5 (62) Ám; width, (42) 45 (50) Ám, from three specimens figured herein.
German specimens. Length, (47) 51 (54) Ám; width, (39) 44 (50) Ám, from six specimens figured herein.
Remarks
The nature of the archaeopyle is problematical. Vozzhennikova (1967, p. 129) stated that "No pylome has been observed". No mention of archaeopyle type was given in Duxbury ( 1977). The Alaskan specimens were interpreted to have a very unconventional archaeopyle "probably formed by the removal or partial detachment of the entire la.cl., 5', 6a-7a, la.s. tabulation sequence" (Wiggins, 1972, p. 299). However, this interpretation is here interpreted to have resulted from compression folds present in the apical horn region of the Alaskan specimens, which, in conjunction with the reduced rugulate parasutural ridges in this region, complicate analysis of the paratabulation (Plate II, 1, 7). This factor also accounts for the variation observed in the length of the apical horn from specimen to specimen. Depending on the angle at which the horn is compressed, both its length and its width may be reduced or increased (e.g. Plate I, 1, 5, 8, compared to Plate I, 6 and Plate II, 8). Truncated apical horns are also encountered, but this is more likely due to mechanical damage than to the development of an excystment structure. Although it was originally believed that the lectotype of N. kostromiensis showed a P3-type archaeopyle, Lentin and Vozzhennikova (1990, pp. 109-110) stated that "One specimen ... has an opening in the cyst wall, however it is impossible to determine if it is a natural opening or if it is the result of damage". Whilst no conclusive proof of archaeopyle type has been found in this study, it appears most likely that an apical archaeopyle may be formed (see Plate I, 10). In addition, the specimen illustrated in PlateII, 7 shows a break in the ectophragm between the dorsal apical and precingular paraplates (B/2, B/3, B/4, K/4, C/5, C/6), although this is only accompanied by a small fracture in the autophragm at this point. It is suggested that excystment in N. kostromiensis may have been achieved via an incomplete development of a (tA) a principal archaeopyle suture, involving all of the pre-apical, apical and accessory ("anterior intercalary") paraplates as a single opercular piece, which remained hinged to the rest of the cyst via the anterior sulcal paraplate. Morphological uncertainties previously resulted in the assignment of this taxon to the family Gonyaulacaceae, subfamily uncertain ( Fensome et al., 1993). Elucidation of the paratabulation now indicates that N. kostromiensis can be assigned to the family Gonyaulacaceae, subfamily Leptodinioideae of Fensome et al. (1993).
Stratigraphic range
Lentin and Vozzhennikova (1990, p. 110) stated that the Russian material is Valanginian in age. In Alaska the species ranges in age from the Valanginian to early Hauterivian, although the youngest occurrence is complicated by an infraNeocomian unconformity ( Wiggins, pers. commun., 1987). The species is also recorded from the supposed Valanginian "bluish grey shale unit" (now the McGuire Formation: Dixon, 1982, p. 4) of the Richardson Mountains in the District of Mackenzie (McIntyre and Brideaux, 1980, plate 4, figs. 2 5), and is characteristic of the Muderongia simplex Oppel-zone of the same age in the Sverdrup Basin (Davies, 1983, p. 11). Duxbury (1977) also provided evidence for a Valanginian age for the species. Riley and Fenton (1984) believed that the taxon did not range higher than strata of Hauterivian age in the Gulf of Mexico, a top datum also recorded byArhus et al. (1986) and Costa and Davey (1992) . However, HeilmannClausen (1987), Harding (1990), Arhus et al. (1990) recorded N. kostromiensis into the lower Barremian strata of Boreal Europe, and Nohr-Hansen (1993) provided a similar range for material from eastern Greenland. Based on the above, the stratigraphic range of this species extends from sediments of Valanginian to earliest Barremian age.
Originally Gonyaulax kostromiensis, subsequently Gonyaulacysta kostromiensis, thirdly (and now) Nelchinopsis kostromiensis.
Tax. sr. synonym of Alaskadinium wigginsii Duxbury, 1977, according to Stover and Williams, 1987.
Duxbury, 1977, retained this species in Gonyaulacysta Deflandre, 1964. Stover and Williams, 1987, retained it in Nelchinopsis.
Holotype: Vozzhennikova, 1967, pl.26, figs.1-6; Jan du Chene et al., 1986, pl.44, figs.7-8; Lentin and Vozzhennikova, 1990, text-fig.64 (lost according to Lentin and Vozzhennikova, 1990)
Lectotype: Lentin and Vozzhennikova, 1990, pl.15, figs.5-6 (designated by Lentin and Vozzhennikova, 1990)
Locus typicus: Kostromsk region, Russia
Stratum typicum: Neocomian, probably Valanginian or Early Hauterivian
Translation Vozzhennikova, 1967: Lees in Sarjeant, 1971(Ed.)
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Nelchinopsis kostromiensis (Vozzhennikova, 1967) Wiggins, 1972, emend. Harding, 1996. According to Harding (1996, p.353,355), Nelchinopsis kostromiensis has an ectophragmal but no autophragmal apical horn. Cyst is holocavate with the maximum separation of wall layers at the parasutures. Ectophragm is minutely perforate and thin. In parasutural areas, ectophragm developed into distally denticulate septa up to 3 µm high in intergonal areas and up to 7 µm at gonal junctions. On apical horn tends to form rugulate ridges. Autophragm laevigate, bearing a dense cover of cylindrical processes up to 0.5 µm in diameter, with length from 1.5 to 7 µm. Paratabulation formula: 2pr, 4', 6", 6c, 6"’, 1p, 1"”, 5s. Apical pattern Q/B, L ventral arrangement. Most likely archeopyle type is t(A)a. Paracingulum well defined, bounded by parasutural septa. Length 51-65 µm.
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Original description: Vozzhennikova, 1967, p. 85-85: Gonyaulax kostromiensis
Theka with a rounded polygonal outline. Epitheca larger than hypotheca and with broadly rounded, coloured, subconical apical horn. The theca may have short processes wich appearently represent the raised up margins to the apical plates. Transverse furrow twisted to the left, its ends seperaed from each other by a distance equivalent to 1 - 1 1/2 times the width of the furrow. The longitudinal furrow either extends to the antapex or is seperated from the antapex by the small accessory plate (npb) which is difficult to distinguish becauce of its ornamentation. Plate formula: on the epitheka 4a + 6np, on the hypotheca 6zd + 1cp, + ?npb + 1a'. The first apical plate does not quite reach the left end of the transverse furrow. The anterior equatorial plates are trapeziform, the sixth being slightly larger smaller than the others. The first posterior equatorial plate is distinguished by its smaller size. Below it lies the small accessory plate. The antapical plate is large and polygonal. The surface of the thecal envelope is densely covered with spines. The margins of the transverse furrow and the plates are fringhed with tall, hyaline, toothed processes. Large spines occur at the angles where the plates join. No pylome has been observed.
Dimensions: holotype - length 61.8 Ám, breadth 50.6 Ám, width of transverse furrow about 6 Ám, length of apical horn 14 Ám. In other specimens length 50.6 - 64.6 Ám, breadth 50.6 -- 56.2 Ám, width of transverse furrow 6 Ám, length of apical horn 8 - 14 Ám, width of toothed processes 6 - 8 Ám.
Revised diagnosis: Wiggins, 1972, p.301
Same as for the genus with the following additional remarks. The 6", 6c 7c, 1p.s., 5'''--6''', 1p, 1p.v., 1'''' tabulation is indicated by fin-like septal membranes which are finely granulose on the lateral surfaces, and sublinear (rare) to dentate or spinose at the external margins. These septal membranes commonly obscure the precise tabulation configuration and plate junctures. The individual plating junctures are suggested by elevated peaks formed at the septal membrane junctures. All plates in this tabulation sequence appear to be ornamented with closely spaced, tubular processes that are slightly flanged or bifurcate? distally, and approximately 1.5--3.0 Ám in length. The 7c cingular plate is small and generally difficult to determine. The relative positions of the longitudinal cingulum membranes appear to be variable. The relative size of the 1''' plate to the 1p plate also appears variable, as determined by their sutural trace insertion into the sulcal region. The insertion point of this trace seems to vary from about midway along the dextral side of the 1p.v. plate to the 1p.s.--1p.v. sutural trace. The relative length of the 5'''--1'''' sutural trace also appears to be quite variable. Although Vozzhennikova (1967, p. 85) indicated a 6''' plate to be present, it was rarely interpreted on the Alaskan specimens, and 5''' is the normal postcingular plate complement. The opercular sequence of plates, the 1a.cl., 5', 6a--7a, 1a.s. series, is indicated by generally faint, low, thin, and smooth ridges. One notable exception to this rule concerns the margins of the 5a plate. The longitudinal margins of this plate are commonly defined by a low, fin-like membrane that is widest at the juncture with the 5" precingular plate and narrowest at the juncture with the 4' apical plate. The maximum width of this membrane is about 1.0--1.5 microns, and decreases proportionally in the apical direction. Occasionally a partition membrane was noted which would separate this 5a plate into platelets, and these are indicated by the notation 5a1 and 5a2. When these membranes are discernible seven anterior intercalary plates can be ascertained. Otherwise, it would be difficult to interpret more than six. The opercular tabulation sequence is ornamented differently than the previous series of plates, and it is obviously two walled in construction. The inner cyst wall is coarsely ornamented with tubular processes, whereas the outer wall is relatively smooth to granulose. This tabulated outer wall forms a distinct apical horn with approximately equal dimensions of base-width and higth. The 1a.cl, apical closing plate, on this horn is unique thickened for this series. The longitudinal traces of the anterior interclaries appear to be coincident with the longitudinal traces of the precingulars except for the 5a-6a trace, but they could be slightly offset from another. Free opercula were encountered, but a few were noted in partial detachment may or not may involve the 1.a.s. plate.
Harding 1996
Nelchinopsis kostromiensis (Vozzhennikova) Wiggins, 1972, emend. nov.
1967 Gonyaulax kostromiensis Vozzhennikova, p. 85, plate 26, figs. 1-6; plate 27, figs. 1, 2. Valanginian.
1969 Gonyaulacysta kostromiensis ( Vozzhennikova)Sarjeant, p. 10.
1972 Nelchinopsis kostromiensis ( Vozzhennikova)-Wiggins, p. 299. Valanginian early Hauterivian.
1977 Gonyaulacysta kostromiensis (Vozzhennikova) Sarjeant, 1969-Duxbury, p. 37. Hauterivian.
1977 Alaskadinium wigginsii-Duxbury, p. 37.
1987 Nelchinopsis kostromiensis ( Vozzhennikova) Wiggins, 1972-Stover and Williams, p. 11.
1990 Nelchinopsis kostromiensis ( Vozzhennikova) Wiggins, 1972-Lentin and Vozzhennikova, p. 108, plate 15, figs. 5, 6 (lectotype).
Emended diagnosis
Leptodinioidean cyst consisting of an autophragm supporting a thin ectophragm on densely-packed, solid, slender processes. Nature of archaeopyle uncertain, possibly apical. Paratabulation fully developed on the ectophragm as indicated by distally denticulate septa, these denticles being pronouncedly elongated in gonal posltions.
Emended description
Shape: Ectophragmal ambitus essentially pentagonal, made angular by the development of parasutural projections at plate triplejunctions. Epicyst bell-shaped with apical plates drawn out into a broad-based, short apical horn. The horn is hollow, distally entire and measures from 9 to 14 Ám in length. The autophragmal ambitus is subspherical and no apical horn is developed on this wall layer. Cyst shows greatest width across posterior cingular suture. Slight primary dorsoventral compression. Epicyst (less apical horn) and hypocyst approximately equidimensional. Cyst is holocavate with the maximum separation of wall layers being found at the parasutures.
Phragma: Ectophragm is minutely perforate and c. 0.2 Ám thick. This appears to consist of partially fused sporopollenin globules (Plate II, 3); in less well preserved specimens the perforations in the layer range from subcircular holes to more sinuous fissures up to several tenths of a Ám long (Plate II, 3, 6). In parasutural areas the ectophragm is developed into distally denticulate septa. The septa are up to 3 Ám in height in intergonal areas, but may attain 7 Ám at gonal triple junctions (Plate I, 1, 4, 7-9; Plate II, 1, 4, 7). The parasutural septa are much reduced on the apical horn, being represented by rugulate ridges usually lacking denticles. Associated with this, the horn is often compressed or collapsed and it can therefore be more difficult to discern paratabulation in the apical region (V. Wiggins, pers. commun.).
The autophragm is laevigate, of sub-micron thickness, and bears a dense cover of cylindrical processes (up to 0.5 Ám in diameter; Plate II, 3). The length of the processes varies from c. 1.5 Ám in intratabular areas up to c. 7 Ám in the case of processes supporting the gonal projections of the parasutural septa. Slight proximal and distal flaring of the processes is observed (Plate II, 3). The junction between individual processes and the ectophragm is not consistently marked on the external cyst surface, although in some cases a small subcircular depression is formed on the exterior of the ectophragm.
Paratabulation: Expressed in the form of denticulate parasutural septa and rugulate ridges (the latter restricted to the apical horn). L-type sexiform gonyaulacoid. Paratabulation formula: 2pr, 4', 6", 6c, 6"', lp, 1"", 5s. Apical pattern is of the Q/B type (Plate II, 2, 7), whereas the ventral region shows the lu/li arrangement (Plate II, 2). The Y/5 suture is clearly longer than the Y/3 suture, indicating an asymmetrical quadrate arrangement of the antapical region. This is an Ornatum-type paratabulation (Helenes, 1986).
Archaeopyle: A clear excystment structure has not been recognised on any of the specimens examined. The available evidence (see below) indicates that the most likely archaeopyle type is (tA)a.
Paracingulum: Well defined, bounded by denticulate parasutural septa of equal height. Laevorotatory, displaced by 1.5-2 cingulum widths.
Parasulcus: L-type arrangement with a narrow, elongate anterior sulcal, prominent flagellar scar and a large, almost circular posterior sulcal (Z) (Plate II, 4, 5).
Dimensions
Russian specimens. Measurements from Lentin and Vozzhennikova (1990). Holotype (lost): length, 62 Ám; width, 51 Ám; apical horn, 14 Ám long. Lectotype: length, 58 Ám; width, 52 Ám. Five remaining specimens: length, 51-65 Ám; width, 51-56 Ám; apical horn, 8-14 Ám long; parasutural septa, 6-8 Ám high.
Alaskan specimens. Range of 50 measured specimens from Wiggins (1972, p. 302): length, (50) 59 (70) Ám; width, (40) 51 (61) Ám, length apical horn, (8) 12 (16) Ám. These measurements are confirmed by new measurements of topotype material provided by Wiggins.
Hunstanton specimens. Length, (57) 59.5 (62) Ám; width, (42) 45 (50) Ám, from three specimens figured herein.
German specimens. Length, (47) 51 (54) Ám; width, (39) 44 (50) Ám, from six specimens figured herein.
Remarks
The nature of the archaeopyle is problematical. Vozzhennikova (1967, p. 129) stated that "No pylome has been observed". No mention of archaeopyle type was given in Duxbury ( 1977). The Alaskan specimens were interpreted to have a very unconventional archaeopyle "probably formed by the removal or partial detachment of the entire la.cl., 5', 6a-7a, la.s. tabulation sequence" (Wiggins, 1972, p. 299). However, this interpretation is here interpreted to have resulted from compression folds present in the apical horn region of the Alaskan specimens, which, in conjunction with the reduced rugulate parasutural ridges in this region, complicate analysis of the paratabulation (Plate II, 1, 7). This factor also accounts for the variation observed in the length of the apical horn from specimen to specimen. Depending on the angle at which the horn is compressed, both its length and its width may be reduced or increased (e.g. Plate I, 1, 5, 8, compared to Plate I, 6 and Plate II, 8). Truncated apical horns are also encountered, but this is more likely due to mechanical damage than to the development of an excystment structure. Although it was originally believed that the lectotype of N. kostromiensis showed a P3-type archaeopyle, Lentin and Vozzhennikova (1990, pp. 109-110) stated that "One specimen ... has an opening in the cyst wall, however it is impossible to determine if it is a natural opening or if it is the result of damage". Whilst no conclusive proof of archaeopyle type has been found in this study, it appears most likely that an apical archaeopyle may be formed (see Plate I, 10). In addition, the specimen illustrated in PlateII, 7 shows a break in the ectophragm between the dorsal apical and precingular paraplates (B/2, B/3, B/4, K/4, C/5, C/6), although this is only accompanied by a small fracture in the autophragm at this point. It is suggested that excystment in N. kostromiensis may have been achieved via an incomplete development of a (tA) a principal archaeopyle suture, involving all of the pre-apical, apical and accessory ("anterior intercalary") paraplates as a single opercular piece, which remained hinged to the rest of the cyst via the anterior sulcal paraplate. Morphological uncertainties previously resulted in the assignment of this taxon to the family Gonyaulacaceae, subfamily uncertain ( Fensome et al., 1993). Elucidation of the paratabulation now indicates that N. kostromiensis can be assigned to the family Gonyaulacaceae, subfamily Leptodinioideae of Fensome et al. (1993).
Stratigraphic range
Lentin and Vozzhennikova (1990, p. 110) stated that the Russian material is Valanginian in age. In Alaska the species ranges in age from the Valanginian to early Hauterivian, although the youngest occurrence is complicated by an infraNeocomian unconformity ( Wiggins, pers. commun., 1987). The species is also recorded from the supposed Valanginian "bluish grey shale unit" (now the McGuire Formation: Dixon, 1982, p. 4) of the Richardson Mountains in the District of Mackenzie (McIntyre and Brideaux, 1980, plate 4, figs. 2 5), and is characteristic of the Muderongia simplex Oppel-zone of the same age in the Sverdrup Basin (Davies, 1983, p. 11). Duxbury (1977) also provided evidence for a Valanginian age for the species. Riley and Fenton (1984) believed that the taxon did not range higher than strata of Hauterivian age in the Gulf of Mexico, a top datum also recorded byArhus et al. (1986) and Costa and Davey (1992) . However, HeilmannClausen (1987), Harding (1990), Arhus et al. (1990) recorded N. kostromiensis into the lower Barremian strata of Boreal Europe, and Nohr-Hansen (1993) provided a similar range for material from eastern Greenland. Based on the above, the stratigraphic range of this species extends from sediments of Valanginian to earliest Barremian age.