310 PROCEEDINGS OF THE ACADEMY OF [1880. 



(Siliceous Clairborne of Hilgard) tbnnation, or what has hitherto 

 been considered as the base of the Eocene formation in South 

 Carolina. Allowing a uniform southerly dip of 10 feet to the 

 mile, these same beds must be about 250 to 280 feet below the 

 "bed of green sand" mentioned by Tuomey (1st Biennial Report, 

 p. 148) as occurring at Baker's Bluff, a few miles above St. 

 Stephens, (stated to be " rich in organic remains, identical with 

 the fossils of Claiborne ") and which, immediately above St. 

 Stephens (Tuomey, Joe cit., p. 149), dips beneath the water-line. 

 This approximate determination of position agrees closely with 

 the observations made in the northeastern portion of the county, 

 for Dr. Smith found by actual barometric measurements that the 

 "chalk hills" (Buhrstone) near Lower Peach Tree on the Ala- 

 bama River, and at a locality about 1 to 8 miles south of Choctaw 

 Corner, were about 250 feet above Knight's and Cave Branches, 

 and the marl bed (No. 2) of Tuomey's Bashia section. 



Whether these older Eocene deposits underly the blufl' at Clai- 

 borne has not yet been proved, but it is but fair to presume that 

 they do. Likewise, it remains to be shown what relation the basal 

 lignite on Bashia Creek bears to the "Northern Lignite" of 

 Hilgard. 



CYTHEREA, Lam. 



Cytherea Nuttalliopsis, n. sp. PI. 20, fig. 1. 



Shell sub-elliptical, moderately ventricose, its surface covered 

 with fine concentric striae, which are apt to become roughly im- 

 bricate on the basal margin ; umbones not very prominent, rather 

 anterior ; lunule cordate, deeply impressed at about its middle, its 

 outline clearly pronounced by a sharply impressed line ; posterior 

 extremity regularly rounded, the anterior somewhat produced ; 

 margin entire ; pallial sinus somewhat angular, pointing toward 

 the centre of the shell. 



Ijength, 1^ inch. Knight's Branch, Clarke Co., Ala. 



This species most resembles among American species of Cy- 

 therea the C. NuttalU, Conr., from which it may be distinguished 

 by the greater production forward of the anterior extremity, and 

 by the median depression in the lunule. In this last character it 

 agrees with G. Poulsoni, Conr., from which, however, it very 

 materially differs in form, and in the much lesser development of 

 the umbones. 



