FROM THE TERTIARY OF VIRGINIA. 21 



Shell, eight-valved ? thick, costate, very much elevated and angular in the back; central area of the intermediate 

 valves with straight, longitudinal, noduliferous ribs, lateral area smooth or nodulose; central area of the terminal 

 valve nodulosely costate, lateral area nodulose. 



Length of valve .15. Breadth do. .50 of an inch. 



Remarks. The ribs of the central area are perfectly parallel, sometimes nearly smooth, 

 and sometimes armed with large nodules in regular series, giving them the appear- 

 ance of being transversely sulcate. The lateral area, in most of my specimens, is 

 smooth, with the exception of two or three impressed lines of growth, but on some there 

 are numerous spherical tubercles, placed without any apparent order. As these are 

 easily removed, I think it probable that all have been furnished with them, but that, in 

 general, they have been obliterated by attrition. They bear some resemblance to the 

 remains of spines. 



This well marked species differs in its sculpture and angulated back from all its 

 congeners. 



This shell is interesting as being the first of its genus found in a fossil state in this 

 country. I believe that but one, the C. Grignonensis, Lam., has been described from the 

 Tertiary of Europe. 



The third figure is a terminal valve, most probably from a young specimen. 



GENUS PATELLA. 

 P. ACINACES, PL. 35. FIG. 36. 



P. testa ovata, valde compressa, falcatd, depressd, crassd, striis concentricis parvis; lineis radiantibus postice 

 f/uatuor; aperturd lineari; apice angulato, recto. 



Shell ovate, very much compressed, falcate, depressed, thick, with small concentric stria:, and four radiating lines 

 posteriorly, mouth linear; apex angular, straight. 



Height .15. Length .55. Breadth .10 of an inch. 



Remarks. The apex is bent forward a little, and somewhat rounded. Diverging from 

 it posteriorly are four elevated lines, two on each side, which may be traced to the base. 

 The aperture is very narrow, almost acute anteriorly and rounded posteriorly. The 

 substance of the shell is extremely thick, particularly at the apex. 



It is not without some hesitation that I have classed this little shell with the genus 

 Patella. Its falcate, compressed shape appears hardly to belong to that genus, and yet 

 is not sufficient to found a new one on. If, however, on farther examination, it should 

 prove distinct, I propose the name of Scaphidium* for it, from its peculiar canoe-like 

 shape. 



FAMILY CALYPTILBHLE. 



GENUS CEMORIA (LEACH.) 

 C. OBLONGA, PL. 35. FIG. 37. 



C. testa conicd, sub-elevatd, tenui, diaphand, costatd; costis longitudinalibus, nodultferis, alternantibiu ; apice pro- 

 ducto, incurvo, anfractu uno> sinistrorsum deflecto, lavi; foramine elliptico; aperturd quadratd, oblongd. 



* A SXOIJH&OC, navigiolum. 





