ventrally with a somewhat gentler slope dorsally. 

 In ventral view the anterior and posterior mar- 

 gins appear square above and below, gently slop- 

 ing to the margin medially. 



Right valve consists of terminal notched cusps, 

 separated by a finely denticulate groove along the 

 dorsal margin. Left valve consists of terminally 

 notched sockets and a finely crenulate bar below 

 the dorsal margin. Line of concrescence and inner 

 margin coincide except along anterior margin 

 where they are widely separated ventrally. Mus- 

 culature that of the genus. 



Dimensions : Holotype : length 0.60 mm ; height 

 0.25 mm ; biconvexity 0.22 mm. 



Occurrence : Lower Peedee only, localities A 

 and F. U.S.N.M. 128995, 128996, 128997, 128998, 

 128999. 



Remarks: This small distinct species occurs 

 only rarely in the subsurface. Female dimorphs 

 are shorter and slightly more tumid than the 

 males. 



Genus Cytheropteron Sars, 1865 



Subgenus Cytheropteron Sars, s. s. 



Cytheropteron (Cytheropteron) penderensis 



Brown, n. sp. 



Plate 6, Figures 12, 13 



Carapace subovate in lateral view ; highest post- 

 erad of midlength; dorsal margin moderately 

 arched; ventral margin straight, slightly sinuous 

 anterad ; anterior margin evenly rounded ; poster- 

 ior margin sharply rounded, extended in a blunt, 

 compressed caudal process. Left valve slightly 

 larger than right. 



Ventral third of valve strongly inflated, topped 

 by a weak sinuous ridge ; inflated portion of valve 

 covers marginal area ; postero-ventral slope sharp- 

 ly truncate. Medially, valves are coursely reticu- 

 late with separating sinuous ridges generally 

 aligned normal to the alate ridge. Hingement and 

 muscle scar that of the genus. 



Dimensions : Holotype : length 0.55 mm ; height 

 0.32 mm ; convexity 0.21 mm. 



Occurrence: Peedee only, localities A and C. 

 U.S.N.M. 129000, 129001. 



Subgenus Eocytheropteron Alexander, 1933 



Cytheropteron (Eocytheropteron) straillis 



Brown, n. sp. 



Plate 6, Figures 14, 15 

 Shell acuminate — ovate in lateral view ; highest 



medially; dorsal margin moderately convex; ven- 

 tral margin straight; anterior margin broadly 

 and evenly rounded; posterior margin narrowly 

 rounded with a blunt compressed caudate exten- 

 sion ventro-medially. Ventral half of valves swol- 

 len, sharply truncate, overhanging or concealing 

 marginal area medially. Anterior third of valves 

 bear three to four subdued ridges parallel to an- 

 terior margin. Median third coarsely punctate 

 with about 20 coarse, widely-spaced pits. 



Hinge in left valve bears an anterior shallow 

 crenulate socket, a long weakly crenulate bar con- 

 necting to a crenulate posterior socket which lies 

 below the marginal area; a very subdued groove 

 separates the interterminal bar from the dorsal 

 margin. Muscle scar that of the genus. 



Dimensions : Holotype : length 0.69 mm ; height 

 0.36 mm. 



Occurrence: Peedee only, localities A, D, and 

 F. U.S.N.M. 129002, 129003. 



Cytheropteron (Eocytheropteron) striatum 



Brown, n. sp. 



Plate 6, Figures 16, 17 



Carapace small, egg-shaped; highest and wid- 

 est medially; dorsal margin gently arched, 

 straight along the hinge line; ventral margin 

 more strongly arched, weakly angulate medially; 

 anterior margin rounded, slightly extended medi- 

 ally ; posterior margin subtriangular, bluntly cau- 

 date medially. Venter is inflated and overhangs 

 margin medially. 



Midportion of valves moderately punctate. Pos- 

 terior third, ventrally, with about four fine widely- 

 spaced ridges on each valve; ridges swing down 

 and forward along the ventral surface, swing up 

 and across the anterior third terminating anterad 

 of the anterior cardinal angle. 



Internal features those of the genus. 



Dimensions : Holotype : length 0.51 mm ; height 

 0.26 mm; biconvexity 0.22 mm. 



Occurrence: Black Creek only, localities G, H, 

 I, J, and K. U.S.N.M. 129004, 129005. 



Genus Velarocythere Brown, n. gen. 

 Type species: Velarocythere scuffeltonensis 

 Brown, n. sp. 



Shell oblong-ovate in lateral view, may be gross- 



20 



