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Trithyrodinium rhomboideum
Trithyrodinium rhomboideum Singh, 1983
Holotype: Singh, 1983, pl.46, fig.11-13
Locus typicus: Dunvegan Formation of the Peace River area
Stratum typicum: Middle Cenomanian
Original description: Singh, 1983, p. 136
Proximate, cornucavate cysts with a rhomboidal body; epipericyst forming a broad, short, and distally rounded apical projection; hypopericyst prolonged into a 5- to 7-micron long, pointed, left antapical horn; right antapical horn rounded, vestigial, and frequently not developed; pericyst smooth, membranous, and transparent; endocyst rhomboidal, dark, and densely ornamented by minute granules or coni; endophragm about 1 micron thick; coni about 0.3 micron wide at the base; endophragm and periphragm closely appressed in the precingular, cingular, and postcingular regions and separated near the bases of the apical and antapical horns forming small pericoels; paratabulation, paracingulum and parasulcus not indicated; archeopyle intercalary, type 3I/3I; operculum free; paraplates la, 2a, and 3a of the endophragm and periphragm released separately; all or some opercular paraplates often remaining in place.
Size range: Length of the pericyst 45(68)83 Ám. Holotype 67 Ám. Breadth of the pericyst 36(45)60 Ám. Holotype 48 Ám. Length of the endocyst 38(60)76 Ám. Holotype 54 Ám. Breadth of the endocyst 36(45)56 Ám. Holotype 48 Ám. Specimens measured: 38.
Affinities:
Singh, 1983, p. 137: Trithyrodinium rhomboideum can be easily distinguished from Trithyrodinium druggii Stone, 1973, which has longer apical and antapical horns and tufts of large granules in the apical and antapical areas of the endocyst. The specimen illustrated as Deflandrea suspecta ( = Trithyrodinium suspectum (Manum and Cookson) Davey, 1969) by Davey (1970, pl. 2, fig. 5) from the early Turonian of Saskatchewan has an endocyst with surface ornamentation similar to that of T. rhomboideum. However, it differs in having an ovoidal endocyst surrounded by a very fragile periphragm and in lacking antapical horns. Davey (pers. comm.) agrees that his specimens are distinct from T. suspectum, which has a much thicker and more complexly structured endophragm, but feels that they are also distinct from T. rhomboideum n. sp. The specimens illustrated as Trithyrodinium sp. A by Norvick (in Norvick and Burger, 1976, pl. 13, figs. 15, 16) from the early Cenomanian of northern Australia are comparable to T. rhomboideum in shape but differ in possessing a paracingulum and very thin, finely granular endophragm and periphragm.
Holotype: Pl. 46, figs. 11-13; slide C-30-Micro. 185, co-ord. 12.2/44.2; sample C-30, section C, Dunvegan Formation.
Holotype: Singh, 1983, pl.46, fig.11-13
Locus typicus: Dunvegan Formation of the Peace River area
Stratum typicum: Middle Cenomanian
Original description: Singh, 1983, p. 136
Proximate, cornucavate cysts with a rhomboidal body; epipericyst forming a broad, short, and distally rounded apical projection; hypopericyst prolonged into a 5- to 7-micron long, pointed, left antapical horn; right antapical horn rounded, vestigial, and frequently not developed; pericyst smooth, membranous, and transparent; endocyst rhomboidal, dark, and densely ornamented by minute granules or coni; endophragm about 1 micron thick; coni about 0.3 micron wide at the base; endophragm and periphragm closely appressed in the precingular, cingular, and postcingular regions and separated near the bases of the apical and antapical horns forming small pericoels; paratabulation, paracingulum and parasulcus not indicated; archeopyle intercalary, type 3I/3I; operculum free; paraplates la, 2a, and 3a of the endophragm and periphragm released separately; all or some opercular paraplates often remaining in place.
Size range: Length of the pericyst 45(68)83 Ám. Holotype 67 Ám. Breadth of the pericyst 36(45)60 Ám. Holotype 48 Ám. Length of the endocyst 38(60)76 Ám. Holotype 54 Ám. Breadth of the endocyst 36(45)56 Ám. Holotype 48 Ám. Specimens measured: 38.
Affinities:
Singh, 1983, p. 137: Trithyrodinium rhomboideum can be easily distinguished from Trithyrodinium druggii Stone, 1973, which has longer apical and antapical horns and tufts of large granules in the apical and antapical areas of the endocyst. The specimen illustrated as Deflandrea suspecta ( = Trithyrodinium suspectum (Manum and Cookson) Davey, 1969) by Davey (1970, pl. 2, fig. 5) from the early Turonian of Saskatchewan has an endocyst with surface ornamentation similar to that of T. rhomboideum. However, it differs in having an ovoidal endocyst surrounded by a very fragile periphragm and in lacking antapical horns. Davey (pers. comm.) agrees that his specimens are distinct from T. suspectum, which has a much thicker and more complexly structured endophragm, but feels that they are also distinct from T. rhomboideum n. sp. The specimens illustrated as Trithyrodinium sp. A by Norvick (in Norvick and Burger, 1976, pl. 13, figs. 15, 16) from the early Cenomanian of northern Australia are comparable to T. rhomboideum in shape but differ in possessing a paracingulum and very thin, finely granular endophragm and periphragm.
Holotype: Pl. 46, figs. 11-13; slide C-30-Micro. 185, co-ord. 12.2/44.2; sample C-30, section C, Dunvegan Formation.