height slightly anterad of median ; dorsal margin 

 strongly arched ; ventral margin convex ; anterior 

 margin evenly rounded, slightly extended ; pos- 

 terior margin angulate, obtuse. 



Left valve larger and overlaps right valve along 

 all margins, overlap most pronounced mid ven- 

 trally. Surface smooth and glassy. Fine denticu- 

 lations on the selvage along anterior and posterior 

 dorsal slopes. Muscle scars not observed. 



Dimensions: Fig. 6: length 1.10 mm; height 

 0.62 mm; biconvexity 0.43 mm. 



Occurrence: Peedee only in outcrop. Swain 

 (1948, p. 193) lists the species from an Eocene 

 interval in the Hammond well. The species has 

 been recognized in water wells from intervals 

 designated as middle and lower Eocene during the 

 present study. Localities A and C. U.S.N.M. 

 128921, 128922, 128923. 



Remarks : This species which occurs with Bair- 

 doppilata pondera Jennings can be most easily 

 distinguished from that species by the larger ratio 

 of length to height and the more pronounced ex- 

 tension of the posterior third of the carapace of 

 B. postextensa. Swain (1948, p. 189) lists the 

 species as occurring in the Eocene interval in the 

 Hammond well at a depth of 1320-1330 feet. 



Family Cytheridae Baird, 1850 



The family Cytheridae has been subjected to 

 recent revision by Sylvester-Bradley (1948, p. 

 794). S-Bradley erected the family Trachyleber- 

 idae to include the genera Trachyleberis Brady 

 and Platycythereis Triebel — genera that are dis- 

 cussed in this paper. Swain (1951, p. 17, 18) and 

 Puri (1953, p. 172, 173) have discussed the re- 

 vision and questioned the validity of the Trachy- 

 leberidae as defined by S-Bradley (1948, p. 793). 

 The present writer feels that a more adequate 

 generic definition of Trachyleberis Brady should 

 preclude its being placed in a new family, and in 

 this paper Trachyleberis Brady is left in the 

 Cytheridae. 



Genus Brachycythere Alexander, 1933 



Brachycythere sphenoides (Reuss) 



Plate 4, Figure 16 



Cythere sphenoides Reuss, 1854, Denschr. K. 

 Akad. Wissen. Wien, vol. 7, p. 141, pi. 26, fig. 2. 

 Alexander, 1929, Texas Univ. Bull. 2907, p. 81, 

 pi. 7, figs. 9, 14. 



Cytheropteron sphenoides (Reuss), Jones and 

 Hinde, 1889, Suppl. Monogr. Cret. Entom. Eng- 

 land, Ireland, Palaeontographical Soc. London, 

 p. 33, pi. 1, figs. 18-20. 



Cytheropteron sp. B., Israelsky, 1929, Arkansas 

 Geol. Survey, Bull. 2, p. 8, pi. 1A, figs. 2a-c. 



Brachycythere sphenoides (Reuss), Alexander, 

 1933, Jour. Paleontology, vol. 7, p. 205, pi. 25, 

 figs. 3a-c, 14a, b ; pi. 26, figs. 7a, b ; pi. 27, fig. 19. 



Brachycythere sphenoides (Reuss) , Swain, 1952, 

 U. S. Geol. Survey Prof. Paper 234-B, p. 80, 

 pi. 8, figs. 42, 43. 

 Dimensions : Fig. 16 : length 0.90 mm ; height 



0.54 mm. 



Occurrence: Black Creek only, localities G, H, 

 I, J, and K. U.S.N.M. 128924. 



Remarks : The external features of this species 

 have recently been described by Swain (1952, p. 

 80). However, specimens from outcrop sections 

 differ slightly but consistently in having one or 

 more fine ridges on the ventral surface. In addi- 

 tion, well preserved specimens have fine spines 

 along the antero-ventral and postero-ventral mar- 

 gins. 



Brachycythere rhomhoidalis (Berry) 

 Plate 4, Figures 5, 8, 9, 10 



Cythere rhomboidalis Berry 1925, Am. Jour. Sci., 

 5th ser., vol. 9, p. 481, figs. 1, 2. 

 Alexander, 1929, Texas Univ. Bull. 2907, p. 86, 

 pi. 7, figs. 1, 2. 



Brachycythere rhomboidalis (Berry) Alexander, 



1933, Jour. Paleontology, vol. 7, no. 2, p. 206. 

 Brachycythere jerseyensis Jennings, 1936, Bull. 



Am. Paleontology, vol. 23, no. 78, p. 48, pi. 6, 



figs. 14a-b. 

 Brachycythere rhomboidalis (Berry) Schmidt, 



1948, Jour. Paleontology, vol. 22, p. 414, pi. 62, 



figs. 8-10. 



Dimensions : Fig. 8 : length 0.95 mm ; height 

 0.47 mm; biconvexity 0.52 mm. 



Occurrence: Peedee only, localities A, B, C, D, 

 E, and F. U.S.N.M. 128925, 128926, 128927, 

 128928. 



Remarks : In outline and in the possession of a 

 deep postjacent furrow at the anterior cardinal 

 angle these specimens resemble Brachycythere 

 sphenoides (Reuss). The present specimens show 

 great variation in the strength of the ventro- 



11 



