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Sumatradinium delectabilis
Sumatradinium? delectabilis de Verteuil and Norris, 1992
NOW Erymnodinium. Originally Sumatradinium, subsequently (and now) Erymnodinium.
De Verteuil and Norris, 1992 questionably included this species in Sumatradinium.
Holotype: de Verteuil and Norris, 1992, pl.9, figs.3-4
Locus typicus: St. Marys Formation, Little Cove Point Beds, 0.5 km south of Little Cove Point (the Ranch Club Section), west shore of Chesapeake Bay, Calvert County, Maryland
Stratum typicum: Late Miocene
Original diagnosis: de Verteuil and Norris, 1992, p. 401
Large protoperidiniacean cysts, compressed dorsoventrally with a convex epicyst and two symmetrical antapical horns. Wall biphragmal; endophragm less than 0.5 µm thick and psilate; periphragm, also thin, bears a fine, evenly distributed reticulum. Tabulation, defined by continuous sutural crests of even height and formed from the periphragm, is peridinioid 4", 3a, ?7", ?c, 5""", 0p, 2"""". Archeopyle hexa 2a, isodeltaform with reduced H3 and H5 sides, may be slightly displaced on the left dorsal epicyst.
Original description: de Verteuil and Norris, 1992, p. 402
The epicyst is broadly convex in dorsoventral view with a rounded apex; it may have a low apical boss 5-7 µm high formed by the confluence of the apical sutural crests. The hypocyst is smaller than the epicyst. It has straight or concave lateral sides and two more or less symmetrical, rounded antapical horns separated by a shallow to moderate depression approximately 3-6 µm deep and about 10-25 µm wide. The endophragm is less than 0.5 µm thick, psilate and closely adpressed to the periphragm. The periphragm bears a fine, even and regular reticulum that appears typical of Sumatradinium. The lumina are roughly circular and 0.5-1.5 µm in diameter; muri are 1 µm in height. Sutural crests are composed of a closely adpressed, folded membrane, and some crests have narrow pandasutural canals at their base. The crests are psilate, sinuous in plan view, and of an even height between 5-8 µm. Plate 4""" is broad and covers most of the dorsal hypocyst. Sutural crests are not developed around plate 2a. The combined effect is that on the dorsal surface the crests appear to be confined to the perimeter of the cyst. The cingulum is marked by two well developed cingular crests and is relatively narrow, while the sulcus is quite broad (upto 20 µm), but indistinct.
Dimensions. Length, 75(83)95 µm; holotype, 85 µm. Equatorial width, 75(88)105 µm; holotype 105 µm. Sutural crests, 5-8 µm. Twelve specimens measured.
Discussion. The distinctive reticulum formed by the periphragm of this species strongly suggests that it is closely related to species of Sumatradinium. It differs most obviously from all known species of Sumatradinium in having continuous sutural crests rather than nontabular or penitabular processes. The new species is provisionally included with Sumatradinium until further data are available regarding the extent and significance of this feature.
NOW Erymnodinium. Originally Sumatradinium, subsequently (and now) Erymnodinium.
De Verteuil and Norris, 1992 questionably included this species in Sumatradinium.
Holotype: de Verteuil and Norris, 1992, pl.9, figs.3-4
Locus typicus: St. Marys Formation, Little Cove Point Beds, 0.5 km south of Little Cove Point (the Ranch Club Section), west shore of Chesapeake Bay, Calvert County, Maryland
Stratum typicum: Late Miocene
Original diagnosis: de Verteuil and Norris, 1992, p. 401
Large protoperidiniacean cysts, compressed dorsoventrally with a convex epicyst and two symmetrical antapical horns. Wall biphragmal; endophragm less than 0.5 µm thick and psilate; periphragm, also thin, bears a fine, evenly distributed reticulum. Tabulation, defined by continuous sutural crests of even height and formed from the periphragm, is peridinioid 4", 3a, ?7", ?c, 5""", 0p, 2"""". Archeopyle hexa 2a, isodeltaform with reduced H3 and H5 sides, may be slightly displaced on the left dorsal epicyst.
Original description: de Verteuil and Norris, 1992, p. 402
The epicyst is broadly convex in dorsoventral view with a rounded apex; it may have a low apical boss 5-7 µm high formed by the confluence of the apical sutural crests. The hypocyst is smaller than the epicyst. It has straight or concave lateral sides and two more or less symmetrical, rounded antapical horns separated by a shallow to moderate depression approximately 3-6 µm deep and about 10-25 µm wide. The endophragm is less than 0.5 µm thick, psilate and closely adpressed to the periphragm. The periphragm bears a fine, even and regular reticulum that appears typical of Sumatradinium. The lumina are roughly circular and 0.5-1.5 µm in diameter; muri are 1 µm in height. Sutural crests are composed of a closely adpressed, folded membrane, and some crests have narrow pandasutural canals at their base. The crests are psilate, sinuous in plan view, and of an even height between 5-8 µm. Plate 4""" is broad and covers most of the dorsal hypocyst. Sutural crests are not developed around plate 2a. The combined effect is that on the dorsal surface the crests appear to be confined to the perimeter of the cyst. The cingulum is marked by two well developed cingular crests and is relatively narrow, while the sulcus is quite broad (upto 20 µm), but indistinct.
Dimensions. Length, 75(83)95 µm; holotype, 85 µm. Equatorial width, 75(88)105 µm; holotype 105 µm. Sutural crests, 5-8 µm. Twelve specimens measured.
Discussion. The distinctive reticulum formed by the periphragm of this species strongly suggests that it is closely related to species of Sumatradinium. It differs most obviously from all known species of Sumatradinium in having continuous sutural crests rather than nontabular or penitabular processes. The new species is provisionally included with Sumatradinium until further data are available regarding the extent and significance of this feature.