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Lithodinia arktika
Lithodinia arktikos Fenton, 1981
Tax. jr. synonym of Lithodinia borealis (Sarjeant, 1980) Riley and Fenton, 1982, according to Riley and Fenton, 1982. See Sarjeant, 1980, for discussionof the latter species.
Holotype: Fenton, 1981, pl.2, fig.2
Age: Late Bathonian
Original description (Fenton, 1981)
Diagnosis: Proximate cyst with spheroidal to ovoidal outline. Paracingulum weakly laevorotatory, subdivision distinct to indistinct. Parasulcus distinct. Surface moderately to coarsely granular with rare spines. Parasutures defined by alignment of spines of low to moderate height, normally becoming distally trabeculate. Archaeopyle apical (?4A). Paratabulation formula ?4', 6", ?6c, 6" ', lp, 1" ", 0--1 pv.
Description: The cyst outline is normally spheroidal, rarely becoming ovoidal. When the apex is present the epi- and hypocyst are of approximately equal proportions. The weakly laevorotatory paracingulum varies between 4 and 7 µm in width, whilst the parasulcus, when observed, is of uniform width. The first postcingular paraplate (1" ') is reduced in size and is sub-quadrate or narrowly rectangular in outline. This paraplate is often difficult to distinguish from the adjacent parasulcal region. The large antapical paraplate may be slightly displaced towards the ventral surface. The autophragra, approximately 1 pm thick, is densely granular or rarely coarsely scabrate with occasional spine development (up to 2 µm high). This imparts a very irregular appearance to the paraplate surfaces. The parasutures are defined by the alignment of spines (2--5 ~m high), which are distally trabeculate, although isolated parasutural spines occasionally occur.
Dimensions: Cyst width 45 (60) 65 µm (16 specimens measured); length 45 (56) 71µm. Holotype: Plate II, 2.
Paratype: Plate II, 1. Type locality: Blisworth Limestone, 99.1 m, Bicker Borehole, Bicker, Lincolnshire, England. "P. retrocostatum" Zone, late Bathonian.
Remarks: Specimens described by Sarjeant (1972) from the late Bathonian of east Greenland were inappropriately assigned to the species L. decapitata (Wetzel 1967) Lentin and Williams 1977. The specimens differ in outline, being predominantly spheroidal, and in the possession of low spinose to trabeculate parasutural ornament, indicating that they are attributable to L. arktikos sp. nov. L. decapitata sensu Wetzel (1967) possesses a definite polygonal outline and much finer, higher perforate parasutural crests. L. decapitata (Wetzel 1967) Lentin and Williams 1977 accords exactly with the diagnosis of L. valensii (published on 20th December 1966), and is considered to be a junior synonym of the latter species. L. decapitata was published on 2nd February 1967, although the publication is dated December 1966. L. arktikos sp. nov. bears a close resemblance to L. callomonii (Sarjeant 1972) Lentin and Williams 1977, differing only in the narrower paracingular width, ventral paratabulation and imperfectly trabeculate parasutural crests of the latter species. L. arktikos sp. nov. also bears a close resemblance to L. cristulata (Sarjeant 1959) Lentin and Williams 1977 and L. caytonensis (Sarjeant
1959} Lentin and Williams 1977, but the latter two species differ in lacking intratabular spines and in possessing perforate parasutural crests. L. arktikos sp. nov. differs from L. bathonica Conway 1978 by possessing
intratabular spines and more prominent trabeculate parasutures. Previous Records: 1972, Sarjeant, late Bathonian, east Greenland. 1974, Herngreen and De Boer, late Bajocian--early Bathonian, The Netherlands.
1978, Fenton and Fisher, early--late Bathonian, northwest Europe.
Derivation of name: Arktikos -- Greek, north, arctic with reference to the first record of the species from east Greenland.
Tax. jr. synonym of Lithodinia borealis (Sarjeant, 1980) Riley and Fenton, 1982, according to Riley and Fenton, 1982. See Sarjeant, 1980, for discussionof the latter species.
Holotype: Fenton, 1981, pl.2, fig.2
Age: Late Bathonian
Original description (Fenton, 1981)
Diagnosis: Proximate cyst with spheroidal to ovoidal outline. Paracingulum weakly laevorotatory, subdivision distinct to indistinct. Parasulcus distinct. Surface moderately to coarsely granular with rare spines. Parasutures defined by alignment of spines of low to moderate height, normally becoming distally trabeculate. Archaeopyle apical (?4A). Paratabulation formula ?4', 6", ?6c, 6" ', lp, 1" ", 0--1 pv.
Description: The cyst outline is normally spheroidal, rarely becoming ovoidal. When the apex is present the epi- and hypocyst are of approximately equal proportions. The weakly laevorotatory paracingulum varies between 4 and 7 µm in width, whilst the parasulcus, when observed, is of uniform width. The first postcingular paraplate (1" ') is reduced in size and is sub-quadrate or narrowly rectangular in outline. This paraplate is often difficult to distinguish from the adjacent parasulcal region. The large antapical paraplate may be slightly displaced towards the ventral surface. The autophragra, approximately 1 pm thick, is densely granular or rarely coarsely scabrate with occasional spine development (up to 2 µm high). This imparts a very irregular appearance to the paraplate surfaces. The parasutures are defined by the alignment of spines (2--5 ~m high), which are distally trabeculate, although isolated parasutural spines occasionally occur.
Dimensions: Cyst width 45 (60) 65 µm (16 specimens measured); length 45 (56) 71µm. Holotype: Plate II, 2.
Paratype: Plate II, 1. Type locality: Blisworth Limestone, 99.1 m, Bicker Borehole, Bicker, Lincolnshire, England. "P. retrocostatum" Zone, late Bathonian.
Remarks: Specimens described by Sarjeant (1972) from the late Bathonian of east Greenland were inappropriately assigned to the species L. decapitata (Wetzel 1967) Lentin and Williams 1977. The specimens differ in outline, being predominantly spheroidal, and in the possession of low spinose to trabeculate parasutural ornament, indicating that they are attributable to L. arktikos sp. nov. L. decapitata sensu Wetzel (1967) possesses a definite polygonal outline and much finer, higher perforate parasutural crests. L. decapitata (Wetzel 1967) Lentin and Williams 1977 accords exactly with the diagnosis of L. valensii (published on 20th December 1966), and is considered to be a junior synonym of the latter species. L. decapitata was published on 2nd February 1967, although the publication is dated December 1966. L. arktikos sp. nov. bears a close resemblance to L. callomonii (Sarjeant 1972) Lentin and Williams 1977, differing only in the narrower paracingular width, ventral paratabulation and imperfectly trabeculate parasutural crests of the latter species. L. arktikos sp. nov. also bears a close resemblance to L. cristulata (Sarjeant 1959) Lentin and Williams 1977 and L. caytonensis (Sarjeant
1959} Lentin and Williams 1977, but the latter two species differ in lacking intratabular spines and in possessing perforate parasutural crests. L. arktikos sp. nov. differs from L. bathonica Conway 1978 by possessing
intratabular spines and more prominent trabeculate parasutures. Previous Records: 1972, Sarjeant, late Bathonian, east Greenland. 1974, Herngreen and De Boer, late Bajocian--early Bathonian, The Netherlands.
1978, Fenton and Fisher, early--late Bathonian, northwest Europe.
Derivation of name: Arktikos -- Greek, north, arctic with reference to the first record of the species from east Greenland.