1881.] NATURAL SCIENCES OF PHILADELPHIA, 419 



P. eboreus Conr. Va. ; N. Gar. 



A. J. Science, xxiii, p, 341. Mioc. Foss., p. 48. 

 P. EolbrooM Rav. Proc. A. K S., ii, p. 96. 



Two. species were included by Conrad under this name, the 

 second being the one subsequently described by Tuomey and 

 Holmes as P. comparilis. 



P. Edgecombensis Conr. N. Car. 



Proc. A. N. S., 1862, p. 291. Not figured. 



The species is described from a specimen in the Smithsonian 

 Institution which I have not had an opportunity to examine. 



P. fraternus Cunr. Va. 



Proc. A. N. S., 1862, p. 291. 

 f P. tricarinatus Cour. A. J. Conchol., ill, p. 189. 



I have not seen a specimen of P. fraternus, but its specific 

 description accords well with the specimen marked in Conrad's 

 handwriting P. tricarinatus, which I have good reason to believe 

 is the very specimen from which the description of P. fraternus 

 has been taken. 



P. Humphrpysii Conr. [OUgocene ?). Md. ; N.J. 



Proceedings of the National Institution, p. 194. 



The convex valve of the average specimens of this species very 

 closely approximates the recent P. laqueatus of Sowerb}'^ 

 (" Thesaurus Conchyliorum," i, p. 46), from the northwest coast 

 of America, both in outline and ornamentation, but differs in the 

 lesser number (only six instead of eight), lesser prominence, and 

 greater irregularity of the ribs, which also spread out broader 

 towards the basal margin. The valve is, moreover, considerably 

 less ventricose than in P. laqueatus. I have been unable to make 

 an}^ comparisons between the opercular valves. 



P. Jeffersonius Say. Md. ; N. Car. ; Va. 



J. A. N. S., iv, p. 133. Conrad, Mioc. Foss., p. 46. 



P. Madisonius Say. Md. ; N. Car. ; Va. 



J. A. N. S., iv, p. 134. Conrad, Mioc. Foss., p. 48. 



P. Magellanicus Gmelin. Md. ; N. Car.; Va. 



Syst. Nat., 3817. 



P. CUntonius Say. J. A. N. S., iv, p. 135. 

 P. princepoides Emmons. N. Car. Geol. Surv., 1858, p. 280. 



I have compared both young and old specimens of the P. CUn- 

 tonius with those of P. Magellanicus, and have no hesitation in 



