218 PROCEEDINGS OF THE ACADEMY OF 



all the specimens,) but, in all the specimens allowing of observation, it is 

 turned in all around, instead of at the anterior portion only, as in c a 1 v a. 

 The external surface also is generally rougher, and the posterior gap smaller, 

 not displaying the bipartite lamina so clearly. Still, as the shells exactly 

 agree in all other respects, it is probable that these differences only result from 

 changes in situation. All the c a 1 v se were taken out of Spondylus ; all the 

 acuminata? were sent loose ; and, from their extremely perfect condition, 

 were probably extracted from clay or wood. If the latter, the irregularities of 

 the decaying timber might cause the roughening of the plate-surface. The ori- 

 ginal specimens of acuminata, however, were taken out of argillaceous lime- 

 stone." 



Specimens in Coll. Acad. Nat. Sci. exhibit intermediate characters. 



** Valves with a single subcentral impressed rib ; the anterior dorsal reflection 

 close-pressed, and furnished with an elevated internal rib. Gray, Ann. and 

 Mag. Nat. Hist. 2d ser. viii. p. 3S3. 



M. curt a, Sowerby. (Sp.) 



Pholas curta, Sowerby, Zool. Proc. p. 71, 1834. Sowerby, Monog. Pholas, 

 Thes. Conch, ii. p. 944, t. 104, f. 33, 34. Hanlev, Desc. Cat. p. 9. 

 Jay, Cat. 4th ed. p. 10. Miiller, Syn. Test. p. 239, t. 108, f. 105. 



Pholadidea curta, Carpenter, Rep. on W. Coast Mollusca. 

 Martesia curta, Gray, Ann. and Mag. viii. p. 384. H. and A. Adams, 

 Genera, ii. p. 331. Chenu, Man. ii. f. 51. Fischer, Journ. Conch. 

 2d ser. iii. 

 Hab. Panama. 

 Coll. Acad. Nat. Sci. Coll. J. C. Jay, M. D. 



M. i n t e r c a 1 a t a, Carpenter. 



Martesia intercalata, Carpenter, Cat. Mnzatlan Shells, p. 13. 

 Hab. Mazatlan. 



M. multistriata, Sowerby. (Sp.) 



Pholas multistriata, Sowerby, Zool. Proc. 1S49. Sowerby, Monog. Pholas. 



Thes. Conch, ii. p. 494, t. 104, f. 35, 36. 

 Martesia multistriata, H. and A. Adams, Genera, ii. p. 331. Fischer, 

 Journ. Conch. 2d ser. iii. p. 52. Gray, Ann. and Mag. Nat. Hist. 2d 

 ser. viii. p. 383. 

 Hab. Australia. 



"Resembling Ph. curta, but the strise on the umbonal part of the anterior 

 are very much finer, and the posterior termination is elongated. The dorsal 

 shield is more oval, rounded anteriorly, and acuminated posteriorly." 

 Sowerby. 



M. obtecta, Sowerby. (Sp.) 



Pholas obtecta, Sowerby, Zool. Proc. 1S49. Sowerby, Monog. Pholas, Thes. 



Conch, ii. p. 496, t. 108, f. SO, 81. 

 Martesia obtecta, Gray, Ann. and Mag. 2d ser. viii. p. 384. H. and A. 

 Adams, Genera, ii. p. 331. Fischer, Journ. Conchyl. 2d ser. iii. p. 52. 

 Hab. Philippines. 



Coll. Acad. Nat. Sci. Coll. G. W. Tryon, Jr. 



The two-lobed dorsal plate, (which from numerous specimens appears to be 

 a permanent character,) together with the greater size of the shell and some 

 difference in the sculpture, are the characters which distinguish this shell 

 from M. m u 1 1 i s t r i a t a ; it would not be surprising, however, if specimens 

 from other localities would prove that this shell is only a well-grown form of 

 mu lti striata. 



[ApriJ ; 



