Shell elongate-elliptical in lateral view, highest 

 medially; dorsal margin gently convex; ventral 

 margin mostly straighter than dorsum, in a few 

 instances, as in illustrated specimen, it is about 

 equal in convexity to dorsum; anterior margin 

 broadly and nearly uniformly rounded ; posterior 

 margin more narrowly rounded, slightly extend- 

 ed medially. Right valve larger, extending beyond 

 left most strongly along dorsum and venter. 

 Valves rather compressed, thickest in posterior 

 half; female dimorphs slightly wedge-shaped in 

 dorsal view, tapering toward anterior. Surface 

 weakly and minutely punctate, a weak sulcus oc- 

 curs mid-dorsally. In mature shells, mid-longitu- 

 dinal section of valve forms a broad ridgelike 

 swelling, in molts swelling is more ventral in po- 

 sition. 



Right valve grooved along dorsum for reception 

 of edge of left; a slight groove lies along ventral 

 margin of right valve; terminally, grooves are 

 barely perceptible. Muscle scar not seen clearly 

 owing to condition of preservation of the present 

 specimens. 



Length of figured specimen (PI. 1, Fig. 1) 0.65 

 mm, height 0.40 mm, convexity 0.25 mm. 



Remarks. — The present specimens were com- 

 pared to hypotypes of Cytherella beyrichi (Reuss) 

 in the U. S. National Museum and found to be 

 different in shape. The specimens identified by 

 Schmidt (1948, p. 406) as C. beyrichi (Reuss) 

 from the Marshalltown and Monmouth Forma- 

 tions of Delaware and Maryland may be the same 

 as the new species. Among other described spe- 

 cies from the Cretaceous, C. kansasensis Morrow 

 from the Late Cretaceous Niobrara Chalk is sim- 

 ilar to C. beyrichoides, n. sp. in elliptical outline, 

 but is apparently less wedge-shaped in dorsal 

 view in the females than is the present species. 



Occurrence. — Lower member of Atkinson For- 

 mation, Humble Oil and Refining Company, No. 1 

 Bennett and Langdale well, Echols County, Geor- 

 gia, core 3,700-3,710 feet. 



Cytherella austinensis Alexander 



Plate 1, Figures 2 a-d 



Cytherella obesa Alexander (not Jones and Kirk- 

 by, 1884), 1929, Univ. Texas Bull. 2907, p. 51, 

 pi. 1, figs. 3, 6. (female, fide Howe and Lauren- 

 cich, 1958, p. 244) 



Cytherella austinensis Alexander, 1929, Univ. 



Texas Bull. 2907, p. 51, pi. 2, figs. 4, 6 (male, 



fide Howe and Laurencich, 1958, p. 244) 

 Cytherella bullata Alexander, 1932, Jour. Paleont., 



v. 6, p. 305, pi. 28, figs. 3, 4 (new name for C. 



obesa Alexander, not Jones and Hinde) 



Loetterle, 1937, Nebr. Geol. Surv. 2nd Sec. Bull., 

 12, p. 50, pi. 8, figs. 4a, b. 



Shaver, 1953, Jour. Paleont., v. 27, p. 471-480, 

 3 figs. 

 ? Cytherella sp. Schmidt, 1948, Jour. Paleont., 



v. 22, p. 406, pi. 61, figs. 4-6. 

 Cytherella cf. C. obesa Alexander, Swain, 1952, 



U. S. Geol. Survey Prof. Paper 224-B, p. 68, 



pi. 8, fig. 2. 



Shell subelliptical in side view, highest at or 

 slightly posterior to midlength; dorsal margin 

 gently convex ; ventral margin nearly straight ; 

 terminal margins nearly equally rounded. Right 

 valve extends strongly beyond left dorsally and 

 ventrally, less strongly terminally; greatest ex- 

 tension is mid-dorsal, where right valve is slightly 

 umbonate. Valves moderately convex, thickest in 

 posterior half. Surface smooth. 



Right valve with strongly incised shelf along 

 dorsal and ventral margins for reception of edge 

 of left; terminally, incisions are much shallower. 

 Muscle scar a large group of radially arranged 

 spots lying anterior to middle. 



Dimorphism exhibited posteriorly by relatively 

 more tumid female shells, in contrast with the 

 more compressed males ; females bear a low broad 

 transverse median interior swelling and a corre- 

 sponding shallow external depression. 



Length of figured specimen (PI. 1, Fig. 2a) 0.69 

 mm, height 0.44 mm, convexity 0.33 mm. . 



Remarks. — The specimens studied here are like 

 C. austinensis Alexander in general shape, and 

 particularly in the rather umbonate right valve; 

 the venter of C. austinensis, perhaps, is more 

 convex than in the present specimens. C. austin- 

 ensis occurs in the upper part of the Austin Chalk 

 and as high as the Pecan Gap Chalk Member of 

 Taylor Marl in Texas (Alexander, 1929, p. 51). 

 Closely related, if not identical specimens were 

 recorded by Schmidt (1948, p. 406) from both 

 the Eocene and the Upper Cretaceous rocks of 

 the Middle Atlantic states. 



Occurrence. — Lower member of Atkinson For- 

 mation, Humble Oil and Refining Company, No. 1 

 Bennett and Langdale well, Echols County, Geor- 

 gia, core 3,690-3,700 and 3,700-3,710 feet; Sun 

 Oil Company, No. 1 Westbury well, Putnam Coun- 

 ty, Florida, core 3,834-3,838 feet. 



j 



