422 PROCEEDINGS OF THE ACADEMY OF [1881. 



a series of much narrower pairs, i. e., the two ribs of each pair 

 arc set closer to each other, and the intervening spaces between 

 the individual pairs is very much greater. The supposed distinc- 

 tion pointed out by Tuomey and Holmes that the number of ribs 

 in P. llortoni is less than in P. Japonicus — namely, forty, whereas 

 in the latter, it is forty -six — does not hold, since the number in 

 P. Japonicus is very variable even in the valves of the same indi- 

 vidual, one specimen showing thirty-four in one valv3, and forty- 

 four in the other. 



P. Peedeensis Tuomey and Holmes. S. Car. 



Plioc. Foss., p. 30. 



P. (Liropecten) Carolinensis Conr. (Kerr's Geol. Report of 

 North Carolina, Appendix, p. 18), appears to be but a variety of 

 this species, having more ribs (twelve). 



This species is stated by Tuomey and Holmes to be " very 

 closely related to, if not identical with P. nodosus of the Gulf of 

 Mexico." It appears to me that the resemblance exists only in 

 the fact of the ribs in both species being knobbed, broken into 

 nodes, otherwise the ornamentation is very distinct, the very 

 prominent radiating ridges on and between the ribs in P. 7iodosus 

 being wanting in P. Peedeensis, where they are replaced b}^ fine 

 impressed lines. 



P. septemnarius Say. S. Car. 



J. A. N. S,, iv, p. 36. Com-., Mioc. Foss., p. 47. 

 Tuomey and Holmes, p. 31. 

 P. Jeffersonius var. ? 



Pecten dislocatus Say, is described from the post-Pliocene 

 deposits of South Carolina by Holmes (" Post-Pliocene Fossils of 

 South Carolina," p. 12), and specimens of P. hevnicyclus from the 

 same deposits, are in the collections of the Academy. Specimens 

 of P. i7'radia7is Linn., distinctly showing the color marks, also 

 occur in the newer formations, but I have been unable to deter- 

 mine the locality or localities whence they have been obtained. 



