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Trithyrodinium dubium
Trithyrodinium dubium C. Singh, 1983
Holotype: C. Singh, 1983, pl.47, fig.8
Age: Middle Cenomanian
Original description (Singh, 1983):
Trithyrodinium dubium n. sp.
Plate 47, figures 8-10
Description: Proximate, bicavate cysts with a subpentagonal and longitudinally elongated outline; apical horn short, blunt; left antapical horn short, conical, and pointed; right antapical horn not developed; pericyst membranous, smooth to finely granular; endocyst dark, subcircular with width greater than length, and in contact with the pericyst in the paracingular region; epipericoel and hypopericoel large; paracingulum slightly helicoidal, 5 to 7 microns wide, and delineated by parallel, transverse, equatorial folds with knobbly margin and equatorial indentations on the lateral margins; parasulcus vaguely outlined as a shallow depression narrowing anteriorly on the ventral hypocyst; posterior parasulcal region sometimes with a slit-like opening (opisthopyle) in the periphragm; periarcheopyle intercalary, type 31; paraplates la, 2a, and 3a released separately; endoarcheopyle intercalary, varying from type 31 (la, 2a, 3a) in some specimens to slightly disarranged paraplates with partially developed archeopyle parasutures in others; some specimens without endoarcheopyle; operculum free; all or some of the opercular paraplates usually remaining in place.
Size range:
Length of the pericyst 70(74)81 microns. Holotype 72 microns.
Breadth of the pericyst 48(53)57 microns. Holotype 51 microns.
Length of the endocyst 34(41)47 microns. Holotype 39 microns.
Breadth of the endocyst 45(52)57 microns. Holotype 51 microns.
Specimens measured 8.
Distribution: Middle Cenomanian. Dunvegan Formation of the Peace River area.
Remarks: An intercalary type 31 periarcheopyle, involving paraplates la, 2a, and 3a, is consistently present in Trithyrodinium dubium n. sp. However, the endoarcheopyle varies from a fully developed 31 (la, 2a, 3a) type to one with partially developed archeopyle parasutures. In some specimens the endoarcheopyle is not developed at all. All or some of the opercular paraplates usually remain in place or are only slightly displaced.
Although T. dubium n. sp. resembles lsabelidinium magnum (Davey) Stover and Evitt, 1978, and lsabelidinium acuminatum (Cookson and Eisenack) Stover and Evitt, 1978, in general appearance, it has been assigned to the genus Trithyrodinium Drugg, 1967, emend. Lentin and Williams, 1976, in the present study, due to the consistent presence of an intercalary 31 (la, 2a, 3a) periarcheopyle.
Holotype: C. Singh, 1983, pl.47, fig.8
Age: Middle Cenomanian
Original description (Singh, 1983):
Trithyrodinium dubium n. sp.
Plate 47, figures 8-10
Description: Proximate, bicavate cysts with a subpentagonal and longitudinally elongated outline; apical horn short, blunt; left antapical horn short, conical, and pointed; right antapical horn not developed; pericyst membranous, smooth to finely granular; endocyst dark, subcircular with width greater than length, and in contact with the pericyst in the paracingular region; epipericoel and hypopericoel large; paracingulum slightly helicoidal, 5 to 7 microns wide, and delineated by parallel, transverse, equatorial folds with knobbly margin and equatorial indentations on the lateral margins; parasulcus vaguely outlined as a shallow depression narrowing anteriorly on the ventral hypocyst; posterior parasulcal region sometimes with a slit-like opening (opisthopyle) in the periphragm; periarcheopyle intercalary, type 31; paraplates la, 2a, and 3a released separately; endoarcheopyle intercalary, varying from type 31 (la, 2a, 3a) in some specimens to slightly disarranged paraplates with partially developed archeopyle parasutures in others; some specimens without endoarcheopyle; operculum free; all or some of the opercular paraplates usually remaining in place.
Size range:
Length of the pericyst 70(74)81 microns. Holotype 72 microns.
Breadth of the pericyst 48(53)57 microns. Holotype 51 microns.
Length of the endocyst 34(41)47 microns. Holotype 39 microns.
Breadth of the endocyst 45(52)57 microns. Holotype 51 microns.
Specimens measured 8.
Distribution: Middle Cenomanian. Dunvegan Formation of the Peace River area.
Remarks: An intercalary type 31 periarcheopyle, involving paraplates la, 2a, and 3a, is consistently present in Trithyrodinium dubium n. sp. However, the endoarcheopyle varies from a fully developed 31 (la, 2a, 3a) type to one with partially developed archeopyle parasutures. In some specimens the endoarcheopyle is not developed at all. All or some of the opercular paraplates usually remain in place or are only slightly displaced.
Although T. dubium n. sp. resembles lsabelidinium magnum (Davey) Stover and Evitt, 1978, and lsabelidinium acuminatum (Cookson and Eisenack) Stover and Evitt, 1978, in general appearance, it has been assigned to the genus Trithyrodinium Drugg, 1967, emend. Lentin and Williams, 1976, in the present study, due to the consistent presence of an intercalary 31 (la, 2a, 3a) periarcheopyle.