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Senegalinium simplex
Senegalinium simplex Lucas-Clark, 2006, p.200–202, pl.3, figs.15–16; pl.4, figs.1–4.
Questionable assignment: Lucas-Clark (2006, p.200).
Holotype: Lucas-Clark, 2006, pl.3, figs.15–16.
Age: Paleocene.
Original description (Lucas-Clark, 2006):
Senegalinium? simplex sp. nov. Plate 3, figs. 15–16; Plate 4, figs. 1–4
Deflandrea rhombohedra McLean, 1971, pl. 12, figs. 1–3. ?Andalusiella rhombohedra (Benson 1976) Stover & Evitt 1978; Edwards et al., 1984, pl. 2, fig. 5.
?Andalusiella rhombohedra of Edwards et al. (1984), Edwards, 2001, pl. 5, fig. 1.
Holotype. Plate 3, figs. 15–16. South Carolina, Savannah River Site, core P18TB, 92.7 m, sample 8656.1934, slide c, CGS Zeiss Sh., coordinates 94.1 × 12.5, England Finder reference N31. Carnegie Museum of Natural History CM 19153.
Derivation of name. From the Latin simplex, meaning simple.
Diagnosis. Small to medium pale peridinioid with thin, pale periphragm and more robust endophragm. Periphragm often lost. Smooth or with fine, irregularly shaped granules on periphragm. short apical and antapical horns. Endoarcheopyle hexagonal 2a, eury delta form; peri-archeopyle difficult to observe. Distinguished by extremely small horns, smooth surface and contrast between thin periphragm and thicker endophragm, clear endoarchopyle. Often found as isolated endocysts.
Description. Small to medium proximate peridinioid, circumcavate cysts, dorsoventrally compressed, with short apical and antapical horns. Antapical horns usually approximately equally developed, or right horn reduced. Endophragm smooth, thicker than periphragm; endocyst ovoidal to peridinioid in shape, often found without enclosing periphragm. Endo- and periphragm may at first appear to be closely appressed except under horns, but careful examination indicates that they are not appressed. Periphragm thin, usually only discernible at the horns; pericyst ovoidal to roundly peridinioid in shape; lateral margins convex; antapical margin slightly concave. Periphragm rarely ornamented with a few granules or denticles randomly scattered; periphragm usually has some folds not related to tabulation except at the cingulum. Tabulation indicated by archeopyle and sometimes by partial cingulum. Other indications of tabulation absent. Archeopyle type I/I (2a), hexagonal, eurydelta form; endoarcheopyle clearly expressed; nature of the periarcheopyle uncertain; endoperculum free, sometimes found within cyst. Cingulum sometimes incompletely indicated by weak folds in periphragm; sometimes indicated by a slight local indentation of the endocyst. Sulcus sometimes indicated by a slight depression of periphragm on ventral hypocyst.
Remarks. This species is difficult to assign to a genus. Although it is questionably assigned to Senegalinium herein, it is circumcavate, and appears to lose the periphragm much of the time, hence its apical pericoel is in communication with the exterior, unlike most species of Senegalinium according to Stover and Evitt (1978, p. 122). It could be assigned to Alterbidinium, but in most cases, the antapical horns are approximately equally developed. Phelodinium is large, has straight to convex sides and is cornucavate. Isabelidinium has an endocyst that is wider than it is long and has a more prominent apical pericoel. Andalusiella has a long antapical horn in the periphragm and a substantial apical horn. Senegalinium? simplex is generally found as isolated endocysts (Plate 4, figs. 3–4). Although it is not certain that the endocyst is the same species, this seems likely because it occurs in the same samples as the cavate cysts, is the same size and shape as the endocysts of the cavate cysts, and has an identical archeopyle.
Dimensions. Length, 40–100 μm; width, 35–90 μm (10 specimens measured).
Comparison. This species is similar to Senegalinium obscurum, but lacks the faint indications of tabulation described and illustrated by Drugg (1967). It also has a less clear cingulum, and lacks denticulation of the cingulum, and grana on the surface of either the endophragm or periphragm are rare or absent. ?Andalusiella rhombohedra is clearly a different species. It has a relatively long antapical horn and substantial apical horn. The overall shape is rhombohedral due to a pronounced difference in the development of the antapical horns, both in the en-docyst and the pericyst. Also, Benson (1976) described and illustrated a ‘microreticulate surficial sculpture’ that is not present in ?Senegalinium simplex sp. nov., and this author did not mention isolated endocysts. However, Benson (1976) considered Deflandrea rhombohedra to be conspecific with Deflandrea rhombohedra of McLean (1971); the latter form is Senegalinium? simplex sp. nov. The pericyst does not extend out into long antapical horns nor a pronounced apical horn, and McLean (1971) stated that the pericyst is often torn, leaving an isolated en-docyst. It differs from Senigalinium? simplex sp. nov. only in having a more pronounced difference in the antapical horns. This is believed to be within the normal range of variation for a species, and questions the use of this character for differentiation between genera. Edwards et al. (1984) and Edwards (2001) illustrated specimens like those of McLean (1971), with a pronounced difference between antapical horns, but otherwise closely resembling Senigalinium simplex sp. nov. Edwards (2001) expressed doubt about her assignment of the specimen to the species of Benson (1976) species by using the term ‘? Andalusiella rhomohedra of Edwards and others1984’. The latter specimen was found in the Ellenton Formation of Georgia, which again suggests it is Senegalinium? simplex sp. nov.
Previously Reported Occurrence. Upper Paleocene, Aquia Formation, Virginia; Paleocene, Ellenton Formation, Georgia.
Occurrence in Present Study. Upper Paleocene, upper Ellenton Formation, Savanna River Site and surrounding area, South Carolina.
Questionable assignment: Lucas-Clark (2006, p.200).
Holotype: Lucas-Clark, 2006, pl.3, figs.15–16.
Age: Paleocene.
Original description (Lucas-Clark, 2006):
Senegalinium? simplex sp. nov. Plate 3, figs. 15–16; Plate 4, figs. 1–4
Deflandrea rhombohedra McLean, 1971, pl. 12, figs. 1–3. ?Andalusiella rhombohedra (Benson 1976) Stover & Evitt 1978; Edwards et al., 1984, pl. 2, fig. 5.
?Andalusiella rhombohedra of Edwards et al. (1984), Edwards, 2001, pl. 5, fig. 1.
Holotype. Plate 3, figs. 15–16. South Carolina, Savannah River Site, core P18TB, 92.7 m, sample 8656.1934, slide c, CGS Zeiss Sh., coordinates 94.1 × 12.5, England Finder reference N31. Carnegie Museum of Natural History CM 19153.
Derivation of name. From the Latin simplex, meaning simple.
Diagnosis. Small to medium pale peridinioid with thin, pale periphragm and more robust endophragm. Periphragm often lost. Smooth or with fine, irregularly shaped granules on periphragm. short apical and antapical horns. Endoarcheopyle hexagonal 2a, eury delta form; peri-archeopyle difficult to observe. Distinguished by extremely small horns, smooth surface and contrast between thin periphragm and thicker endophragm, clear endoarchopyle. Often found as isolated endocysts.
Description. Small to medium proximate peridinioid, circumcavate cysts, dorsoventrally compressed, with short apical and antapical horns. Antapical horns usually approximately equally developed, or right horn reduced. Endophragm smooth, thicker than periphragm; endocyst ovoidal to peridinioid in shape, often found without enclosing periphragm. Endo- and periphragm may at first appear to be closely appressed except under horns, but careful examination indicates that they are not appressed. Periphragm thin, usually only discernible at the horns; pericyst ovoidal to roundly peridinioid in shape; lateral margins convex; antapical margin slightly concave. Periphragm rarely ornamented with a few granules or denticles randomly scattered; periphragm usually has some folds not related to tabulation except at the cingulum. Tabulation indicated by archeopyle and sometimes by partial cingulum. Other indications of tabulation absent. Archeopyle type I/I (2a), hexagonal, eurydelta form; endoarcheopyle clearly expressed; nature of the periarcheopyle uncertain; endoperculum free, sometimes found within cyst. Cingulum sometimes incompletely indicated by weak folds in periphragm; sometimes indicated by a slight local indentation of the endocyst. Sulcus sometimes indicated by a slight depression of periphragm on ventral hypocyst.
Remarks. This species is difficult to assign to a genus. Although it is questionably assigned to Senegalinium herein, it is circumcavate, and appears to lose the periphragm much of the time, hence its apical pericoel is in communication with the exterior, unlike most species of Senegalinium according to Stover and Evitt (1978, p. 122). It could be assigned to Alterbidinium, but in most cases, the antapical horns are approximately equally developed. Phelodinium is large, has straight to convex sides and is cornucavate. Isabelidinium has an endocyst that is wider than it is long and has a more prominent apical pericoel. Andalusiella has a long antapical horn in the periphragm and a substantial apical horn. Senegalinium? simplex is generally found as isolated endocysts (Plate 4, figs. 3–4). Although it is not certain that the endocyst is the same species, this seems likely because it occurs in the same samples as the cavate cysts, is the same size and shape as the endocysts of the cavate cysts, and has an identical archeopyle.
Dimensions. Length, 40–100 μm; width, 35–90 μm (10 specimens measured).
Comparison. This species is similar to Senegalinium obscurum, but lacks the faint indications of tabulation described and illustrated by Drugg (1967). It also has a less clear cingulum, and lacks denticulation of the cingulum, and grana on the surface of either the endophragm or periphragm are rare or absent. ?Andalusiella rhombohedra is clearly a different species. It has a relatively long antapical horn and substantial apical horn. The overall shape is rhombohedral due to a pronounced difference in the development of the antapical horns, both in the en-docyst and the pericyst. Also, Benson (1976) described and illustrated a ‘microreticulate surficial sculpture’ that is not present in ?Senegalinium simplex sp. nov., and this author did not mention isolated endocysts. However, Benson (1976) considered Deflandrea rhombohedra to be conspecific with Deflandrea rhombohedra of McLean (1971); the latter form is Senegalinium? simplex sp. nov. The pericyst does not extend out into long antapical horns nor a pronounced apical horn, and McLean (1971) stated that the pericyst is often torn, leaving an isolated en-docyst. It differs from Senigalinium? simplex sp. nov. only in having a more pronounced difference in the antapical horns. This is believed to be within the normal range of variation for a species, and questions the use of this character for differentiation between genera. Edwards et al. (1984) and Edwards (2001) illustrated specimens like those of McLean (1971), with a pronounced difference between antapical horns, but otherwise closely resembling Senigalinium simplex sp. nov. Edwards (2001) expressed doubt about her assignment of the specimen to the species of Benson (1976) species by using the term ‘? Andalusiella rhomohedra of Edwards and others1984’. The latter specimen was found in the Ellenton Formation of Georgia, which again suggests it is Senegalinium? simplex sp. nov.
Previously Reported Occurrence. Upper Paleocene, Aquia Formation, Virginia; Paleocene, Ellenton Formation, Georgia.
Occurrence in Present Study. Upper Paleocene, upper Ellenton Formation, Savanna River Site and surrounding area, South Carolina.