222 



I'rus ; and anotlier specimen of lime mixed with argil, in whicli 

 the progress of three JSaxicavas was arrested by a thin layer purely 

 argillaceous. 



Petricola pholadiformis, Lam., An. sans Yetehr., vol. 5, 

 p. 505. Sowerhy's Genera, pi. Petricola, fig. \ and 2. ConracTs 

 Marine shells, pi 7. Desk. Enc. Metli. p. 747. 



Petricola fornicata, S. Journ. Acad. Nat. Sci., vol. 2, p. 319. 



Ohs. This shell may be truly said to be an extraordinary species, 

 having the deceptive exterior aspect of a Pholas, and like many of 

 that genus residing in cavities drilled out of the most compact 

 earth, as is also sometimes the case with the P. ochroleuca. Lam. 



It is abundant on many parts of our coast from Maine to Florida. 

 Dr. Eavenel sent me specimens from Charleston, and Dr. Storer 

 informs me that it is common at Chelsea and Martha's Vineyard in 

 Massachusetts. Plate 60, fig. 1. 



Petricola dactylus, Sowb. — Desc. Shell transversely oblong- 

 oval, white, with radiating raised striae, which on the posterior 

 half of the shell, from twelve to eighteen in number, are larger, 

 and approximate, those of the anterior portion of the shell, filifonn, 

 the transverse striae are undulated on the anterior part of the 

 shell ; basal margin arquated ; teeth two in the right valve and one 

 prominent one in the left. 



Petricola dacti/liis, Sowerb?/'s Genera, pi. Petricola, fig. 3. 



Ohs. For this species I am indebted to the kindness of Dr. 

 Ravenel, who distinguished it from the preceding as a separate 

 species. The largest specimen in my possession measures nearly 

 two inches in breadth. It resembles ih.eplioladiformis,\)Vit\BO. 

 more robust shell, being less transversely elongated, the base more 

 arquated, the larger striae are more numerous and destitute of 

 vaulted scales, and the teeth are quite different. I had distin- 

 guished it by the name ai flagellata, but on a more close compari- 

 son with Sowerby's figure and very short description, in which no 

 locality is given, it evidently approaches that species, and is pro- 

 bably identical. PI. 60, fig. 2. 



Cryptostoma. — Shell ear-shaped, univalve, spiral, very much 

 depressed ; spire hardly elevated above the general curvature, 

 lateral ; aperture very large, oblong, entire, embracing a portion of 

 the preceding volution } labrum simple ; volutions two or three ; 



