valve consists of a high pointed tooth and subja- 

 cent socket connected to a finely crenulate inter- 

 terminal groove, formed along the thickened dor- 

 sal margin, connecting posteriorly to an elongate 

 carved tooth which lies above the groove. Hinge of 

 the left valve the antithesis of the right. Inner 

 margin and line of concrescence coincident. An- 

 terior margin with about ten widely spaced simple 

 pore canals; posterior margin bears about six. 

 Hinge teeth and sockets noncrenulate. Muscula- 

 ture that of the genus. 



Dimensions: Fig. 15: female; length 0.54 mm; 

 height 0.32 mm; biconvexity 0.28 mm. 



Fig. 16: male; length 0.63 mm; 

 height 0.29 mm ; biconvexity 0.27 mm. 



Occurrence: Black Creek throughout and low- 

 ermost Peedee only, localities A, C, G, H, I, and J. 

 U.S.N.M. 128947, 128948, 128949, 128950, 128951. 



Remarks: The present specimens are slightly 

 more acute posteriorly and the ventral and median 

 ridges terminate approximately along the same 

 vertical line, otherwise they are conspscific with 

 C. gapensis Alexander. Sexual dimorphism is 

 marked with male dimorphs being nearly one- 

 third longer than the females. 



Trachyleberis (?) praecursora Brown, n. sp. 



Plate 7, Figures 20-25 



Carapace small, subrhomboidal in lateral view ; 

 dorsal margin straight; ventral margin straight 

 to concave medially ; anterior margin broadly and 

 evenly rounded ; posterior margin angulate, 

 pointed. 



Anterior margin strongly and finely denticulate 

 with about 20 spines, more pronounced ventrally ; 

 posterior margin with about four blunt spines 

 ventrally; a short ridge, highest posterad, rises 

 near the antero- ventral junction, extends adjacent 

 to and above the ventral margin, swings gently 

 inward medially, and terminates above abruptly 

 compressed posterior ; a faint dorsal ridge, high- 

 est posteriorly, commences postjacent to a sub- 

 dued eye tubercle, outlines the dorsal margin 

 above, turns inward posterad, and terminates 

 above compressed anterior ; a median ridge com- 

 mences in the anterior third, ventrally. passes 

 through the inflated subcentral node and connects 

 to the dorsal ridge posteriorly. Surface, medially, 

 is discretely reticulate, anterior and posterior 

 thirds smooth. 



Hinge in right valve a high ovate pointed tooth 



and large ovate postjacent socket, long interter- 

 minal bar terminating in a weak elongate socket 

 connected to a high rounded tooth formed at out- 

 ward inflation of marginal area ; left valve an- 

 tithesis of right. Inner margin and line of con- 

 crescence coincide, not perfectly coincident along 

 anterior ; deep subcentral depression. Musculature 

 that of the genus. 



Dimensions : Holotype : length 0.53 mm ; height 

 0.28 mm; biconvexity 0.20 mm. 



Occurrence: Lower Peedee only. This species 

 apparently occurs only in the Exogyra cancellata 

 subzone, localities A and F. U.S.N.M. 128952, 

 128953, 128954, 128955, 128956, 128957. 



Remarks : Female dimorphs can be distinguish- 

 ed by their relatively shorter and broader cara- 

 paces. The species is provisionally placed in Tra- 

 chyleberis Brady because of slight differences in 

 hingement from that given for Trachyleberis 

 Brady. Our specimens show a slight swelling 

 (secondary tooth?) at the anterior end of the 

 interterminal bar in the left valve and a corre- 

 sponding shallow socket in the right valve. Com- 

 parison with Toulmina Munsey (Munsey, 1953, 

 p. 6) may show our species to belong to that genus. 



Genus Platycythereis Triebel, 1940 



Platycythereis costatana angula (Schmidt) 



Plate 6, Figures 22-25 



Cythereis costatana angula Schmidt, 1948, Jour. 

 Paleontology, vol. 22, p. 420, pi. 61, figs. 17- 

 18. 



Paracythereis semilenis Schmidt, 1948, Jour. 

 Paleontology, vol. 22, p. 418, pi. 61, fig. 14. 



Carapace subquadrate in side view ; dorsal mar- 

 gin straight to slightly convex; ventral margin 

 straight ; anterior margin broadly and evenly 

 rounded, strongly and broadly rimmed, spinose; 

 posterior margin compressed, subtriangular, 

 sharply rounded, weakly rimmed, spinose. 



Rounded ridge, reticulate anterad — punctate 

 posterad, extends from just behind anterior dor- 

 sal angle back along dorsal margin to posterior 

 dorsal angle, turns at right angles, and extends 

 parallel to and above dorsal third of compressed 

 posterior. A second short ridge extends from just 

 anterad of midlength back along ventral margin 

 to posterior ventral angle, turns at right angles, 

 and extends parallel to and above ventral third of 

 compressed posterior. Posterior margin with 

 about six well developed spines on dorsal third. 



15 



