222 
irus ; and another specimen of lime mixed with argil^ in which 
the progress of three Saxicavas was arrested by a thin layer purely 
argillaceous. 
Petricola pholadieormis, Lam.j An. sans Vetehr., vol. 5, 
p. 505. Sowerh^’s Genera, pi. Petricola, Jig. 1 and 2. Conrad^ s 
Marine shells, pi. Jl . Desh. Enc. Meth. 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. ochroleuea, Lam. 
It is abundant on many parts of our coast from Maine to Florida. 
Dr. Ravenel 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, filiform, 
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 dactylus, Soiverhy’s Genera, pi. Petricola, Jig. 3. 
Ohs. For this species I am indebted to the kindness of Dr. 
Havenel, who distinguished it from the preceding as a separate 
species. The largest specimen in my possession measures nearly 
two inches in breadth. It resembles ihe plioladiformis,hViii^ 2^ 
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 of Jlagellata, 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. 
Crypto STOMA. — 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 ; 
