FROM THE TERTIARY OF VIRGINIA. 23 



by Mr. Broderip, says, " L'animal des Calyptrees et des Crepidules nous parait ne dif- 

 ferer en rien d'essentiel ; et quant a la cloison du test, soit que cette cloison soit trans- 

 versale, soit qu 'elle ne consiste qu 'en lamelles anexees au fond de la coquille, elle pre- 

 sente des passages de ces deux etats, et ne peut servir qu 'a etablir des simples sous- 

 genres, au grand genre Calyptrsea ou Crepidula comme on voudrait 1'appeler." I have 

 therefore put the following shells as merely in sub-genera. 



SUB-GENUS INFUNDIBULUM (D E MONTFORT.) 

 I. CONCENTRICUM, PL. 35. FIG. 39. 



1, testa patdliformi, deprcsso-ccmicd, tenui, simplici; lineis minutis concentricis; apice centrali, anfractu parvo uno; aper- 

 turd sub-rotunda; cyatho recto, varice marginato. 



Shell patclliforra, depressed-conical, thin, simple; with minute concentric lines; apex central, with one small 

 whorl; aperture sub-rotund; cyathus straight, margined with a varix. 



Diam. .22. Height .09 of an inch. 



Remarks. This shell is entirely simple and patelliform, with the exception of one 

 small whorl at the apex. The cyathus is flat and straight, extending from the centre to 

 the margin, with a thick varix at its outer edge. 



The only Infundibulum, to which this is allied, is the I. centrale, Con., but that 

 species is described as ovate, while this is conical, or even slightly concave. 



This is one of the shells that show the gradual passage from the Infundibulum to the 

 Crepidula, and the propriety of uniting these genera. Its want of whorls, and the con- 

 centric lines of growth, seem to place it in the Calyptrseee, while the cyathus constitutes 

 it an Infundibulum. 



SUB-GENUS CREPIDULA. 

 C. PONDEROSA, PL. 35. FIG. 40. 



C. testa sub-globosd, crassissimd, ponderosd, convolutd, rugosd; sulco prope suturam lato, minime prof undo; suturd parvd; 

 apice vohtto, rotundato, anfractibus sesqui; aperturd arctato ellipticd; cyatho crassissimo, undulato, acie Jlexuosd, vix aperturte 

 dimidiam aquante. 



Shell sub-globose, very thick, ponderous, whorled, rugose; with a wide, shallow sulcation near the suture; suture 

 small; apex voluted, rounded, with a whorl and a half; mouth narrow-elliptical; cyathus very thick, undulate, with 

 a flexuose edge; scarcely half the length of the mouth. 



Height 1.15. Length 1.90. Breadth 1.50 inches. 



Remarks. There are occasional irregular lines of growth over the surface. The sul- 

 cation near the suture is sometimes scarcely perceptible. It usually continues for about 

 one third of a whorl from the aperture, and then becomes obsolete. The mouth is some- 

 times very small and nearly round. The cyathus is extremely solid with two depres- 

 sions on its surface and a waved edge. It is deeply set in the shell, and disappears 

 gradually into the sides, so that its margin cannot be traced. The apex is more voluted 

 than in any species of Crepidula that I have met with. 



This fine shell has, most probably, been heretofore confounded with the C. costata, 

 Morton, as it is too common and too conspicuous to have escaped observation, and as there 

 are specimens of both under that name in the collection of the Academy of Natural 

 F 



