495 



costata, costis serratis, margine ventrali bevigato, rotundato ; pos- 

 tice prope medium concentrice striata, extremitate plus minusve, at- 

 tenuate ; laminis tribus, una. elongata ad margines ventrales, una 

 inter margines dorsales, una magna, subquadrata, postice emargi- 

 nata, super umbones posita. 



An enclosed species, with the dorsal part of the anterior ribbed 

 angularly by raised, serrated ridges. The posterior portion is con- 

 centrically striated, and at the termination indefinitely extended. 

 There is a thin, long plate between the dorsal margins, and another 

 over the ventral margins. The umbonal shield is large, rather 

 quadrate, and at the posterior edge emarginated. 



Pound on the coasts of Great Britain, and in floating wood in 

 various parts of the Atlantic. Mr. Cuming has collected varieties 

 at the Philippine Islands. 



30. Pholas cuneieormis (pi. civ. f. 38,39, pi. cviii. f. 86,87), 

 Say, Journ. Ac. Sci. Philad. vol. ii. p. 322. 



Ph. testa oblonga, clausa, transverse oblique divisa ; antice mar- 

 gine ventrali laevigata, rotundato, latere dorsali costis longitudina- 

 libus arcuatis, serratis ; postice concentrice striata, plus minusve 

 attenuate,; laminis tribus, una elongata ad margines ventrales, 

 una inter margines dorsales, una ad umbones antice obtuse angu- 

 lata, postice acuminata. 



Besembling PA. striata (f. 40, 41, 42, 43, 44), but with the 

 stria?, or ribs, of the anterior part curved, not angular, and the 

 dorsal slueld smaller, and pointed at each end. 



N. America. 



31. Pholas semicostata (pi. cviii. f. 84, 85), (copied), Lea, 

 Pro. Bost. Soc. Nat. Hist., Nov. 1814, pi. 24. f. 1. 



Ph. testa Ph. cuneiformi simillima, sed magis pyriformi ; laminis 

 marginalibus nullis ? 



This may possibly may be identical with Ph. cuneiformis, or 

 with Ph. striata, but it is more ventricose, and no marginal plates 

 are mentioned in the description. 



It is a very small shell, inhabiting the coasts of South Carolina. 



32. Pholas corticakia (pi. cviii. f. 94, 95, 96), Gray, MS. 

 Brit. Mus. 



Ph. testa clausa, divisa; antice angulatim longitudinaliter costata, 

 costis serratis, margine ventrali la-vigato ; postice prope medium 



3 s 2 



