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Pareodinia osmingtonensis
Pareodinia osmingtonensis (Sarjeant, 1962) emend. Wiggins, 1975
Now Pluriarvalium. Originally (and now) Pluriarvalium, subsequently Pareodinia. Stover and Evitt, 1978 and Lentin and Williams, 1989 retained this species in Pluriarvalium Sarjeant, 1962.
Holotype: Sarjeant, 1962, pl.1, fig.5
Locus typicus: Osmington Mills, Dorset, England
Stratum typicum: Late Oxfordian
Original diagnosis: Sarjeant, 1962, p.262: Pluravalium osmingtonense
A species of Pluriarvalium having an ovoidal theca with well developed apical horn, a narrow transverse and broader longitudinal furrow, the latter with a relatively brief hypothecal extension. The sutures and furrow marginsbearlow crests from which short, simple spines arise. Tabulation: ? 5", 2a, 6", 6""", 1p, 1pv, ?7pc, 1"""". Plate 1""" is reduced.
Dimensions: Holotype: Overall length 115µm; length of horn 23µm;overall breadth 75µm; sutural spines ca. 1µm in length. Range: overall length 100-125µm.
Emended diagnosis: Wiggins, 1975, p. 105
Proximate fossil cysts, ambitus ovoidal, epitract and hypotract approximately equal. Cyst exhibits an apical horn and a broadly rounded antapex. Reflected tabulation distinctly evident and includes possible series formula of 7a.cl., 6", 6a, 6", 7c, 7""", 3"""", plus an uncertain number of sulcal platelets and posterior intercalary plares. Sutures indicated by low to moderate relief septal structures that may be sublinear, minutely dentate", fimbriate, or setose lineaments. Archeopyle intercalary and may be either Type I or Type 3I. Cyst wall ornamentation varies from smooth to finely granulate. Apicular structure commonly present in the form of a short rod or small apical wall thickening. Kalyptra occasionally evident and usually fragmental; it obscures septal structures.
Although tabulation is well expressed by septal structures, these structures hinder the seriation analysis of such an involved and complex pattern. No single specimen has yielded a complete tabulation pattern, and several hundred specimens were examined to produce the postulated cyst diagram (Text-fig. 7). The small apical closing plates of the preapical series are well established and probably 7 in number. What has been interpreted as an equivalent series on other species of Pareodinia has been inferred from the study of this species. The apical horn on some specimens of Pareodinia ceratophora exhibits a distinct wall thinning or notching in this corresponding area. However, the numerical sequence and exact pattern of this sequence is poorly known. When present, apicular structures are associated with this series.
Between the preapical and intercalary series are 6 rather elongate apicals, and the length and pattern of this series is obviously dependent upon the amount of apical horn prolongation. What happens to the preapical and apical series when a horn is foreshortened is unknown.
The intercalary series appears to consist of 6 plates. The unusual location of the 5a could be considered as a portion of the 5" precingular, and thus only 5 intercalaries could be interpreted. However, a septal lineament corresponding to the 5a-5" juncture is not uncommonly evident, and this feature is illustrated as a ridge on figure 4 of Plate 4. Sarjeant (in Davey, et al. 1966, p. 156) has suggested that the archeopyle may occur by the loss of the anterior ventral surface. On the other hand, I believe that it is intercalary. This archeopyle is formed when the 2a, and sometimes 1a-3a, are discarded. Because the 1a and 3a plates are small on this species, it is usually difficult to ascertain if they are truly missing.
Six precingular plates are usually evident on this species along with at least 6 postcingulars, but at this point we must allow for a certain amount of subjectivity in interpretation. The sulcal area, the balance of the hypotract, and part of the cingulum present an extremely complicated series of small plates, each bounded by septa that are somewhat optically overlapping. There is apparently an almost double row or series of small plates between the postcingulars and antapicals. Sarjeant encountered a similar difficulty with the tabulation of the hypotract.
The antapex has 3 very small plates that appear to be almost imperceptibly thickened, and we have chosen to interpret these as the 3"""" antapical sequence. However, this could be in error because of axial alignment, and a 2"""" or 4"""" antapical series is possible. In spite of this, a 1"""" interpretation for this series is highly doubtful.
Now Pluriarvalium. Originally (and now) Pluriarvalium, subsequently Pareodinia. Stover and Evitt, 1978 and Lentin and Williams, 1989 retained this species in Pluriarvalium Sarjeant, 1962.
Holotype: Sarjeant, 1962, pl.1, fig.5
Locus typicus: Osmington Mills, Dorset, England
Stratum typicum: Late Oxfordian
Original diagnosis: Sarjeant, 1962, p.262: Pluravalium osmingtonense
A species of Pluriarvalium having an ovoidal theca with well developed apical horn, a narrow transverse and broader longitudinal furrow, the latter with a relatively brief hypothecal extension. The sutures and furrow marginsbearlow crests from which short, simple spines arise. Tabulation: ? 5", 2a, 6", 6""", 1p, 1pv, ?7pc, 1"""". Plate 1""" is reduced.
Dimensions: Holotype: Overall length 115µm; length of horn 23µm;overall breadth 75µm; sutural spines ca. 1µm in length. Range: overall length 100-125µm.
Emended diagnosis: Wiggins, 1975, p. 105
Proximate fossil cysts, ambitus ovoidal, epitract and hypotract approximately equal. Cyst exhibits an apical horn and a broadly rounded antapex. Reflected tabulation distinctly evident and includes possible series formula of 7a.cl., 6", 6a, 6", 7c, 7""", 3"""", plus an uncertain number of sulcal platelets and posterior intercalary plares. Sutures indicated by low to moderate relief septal structures that may be sublinear, minutely dentate", fimbriate, or setose lineaments. Archeopyle intercalary and may be either Type I or Type 3I. Cyst wall ornamentation varies from smooth to finely granulate. Apicular structure commonly present in the form of a short rod or small apical wall thickening. Kalyptra occasionally evident and usually fragmental; it obscures septal structures.
Although tabulation is well expressed by septal structures, these structures hinder the seriation analysis of such an involved and complex pattern. No single specimen has yielded a complete tabulation pattern, and several hundred specimens were examined to produce the postulated cyst diagram (Text-fig. 7). The small apical closing plates of the preapical series are well established and probably 7 in number. What has been interpreted as an equivalent series on other species of Pareodinia has been inferred from the study of this species. The apical horn on some specimens of Pareodinia ceratophora exhibits a distinct wall thinning or notching in this corresponding area. However, the numerical sequence and exact pattern of this sequence is poorly known. When present, apicular structures are associated with this series.
Between the preapical and intercalary series are 6 rather elongate apicals, and the length and pattern of this series is obviously dependent upon the amount of apical horn prolongation. What happens to the preapical and apical series when a horn is foreshortened is unknown.
The intercalary series appears to consist of 6 plates. The unusual location of the 5a could be considered as a portion of the 5" precingular, and thus only 5 intercalaries could be interpreted. However, a septal lineament corresponding to the 5a-5" juncture is not uncommonly evident, and this feature is illustrated as a ridge on figure 4 of Plate 4. Sarjeant (in Davey, et al. 1966, p. 156) has suggested that the archeopyle may occur by the loss of the anterior ventral surface. On the other hand, I believe that it is intercalary. This archeopyle is formed when the 2a, and sometimes 1a-3a, are discarded. Because the 1a and 3a plates are small on this species, it is usually difficult to ascertain if they are truly missing.
Six precingular plates are usually evident on this species along with at least 6 postcingulars, but at this point we must allow for a certain amount of subjectivity in interpretation. The sulcal area, the balance of the hypotract, and part of the cingulum present an extremely complicated series of small plates, each bounded by septa that are somewhat optically overlapping. There is apparently an almost double row or series of small plates between the postcingulars and antapicals. Sarjeant encountered a similar difficulty with the tabulation of the hypotract.
The antapex has 3 very small plates that appear to be almost imperceptibly thickened, and we have chosen to interpret these as the 3"""" antapical sequence. However, this could be in error because of axial alignment, and a 2"""" or 4"""" antapical series is possible. In spite of this, a 1"""" interpretation for this series is highly doubtful.