INSTITUTE OF SCIENCE, PHILADELPHIA. 357 



From the variety cyinba:fonins the recent C. convexa Say is derived, but 

 earher than the Pliocene ; the intergrading is too close to permit us to separate 

 the specimens specifically. 



Crepidula convexa Say. 

 C. convexa Say, Journ. Acad. Nat. Sci. Phila. ii. p. 227, 1822. 



Newer Pliocene of the Myakka River, Fla., Willcox ; Post-Pliocene of 

 Sankoty Head, Mass., Verrill, and of North Creek, Fla., Dall and Willcox ; 

 and of Simmons's Bluff, South Carolina, Burns; living on the coasts of the 

 United States from Nova Scotia to East Florida, and west on the north shore 

 of the Gulf to Galveston. 



There is a flat form of convexa growing on flat stones or oysters which 

 much resembles that mutation of C.fornicata which Say called glaiica, and 

 the name of glauca has been applied to it, notwithstanding that Say's descrip- 

 tion in speaking of the indented edge of the septum of glauca (which in con- 

 vexa is straight) shows that the shell he had in mind was not convexa, at any 

 rate. Even if the two names were founded on mutations of a single species, 

 since they were printed simultaneously, it would be better to retain of the 

 two the much more characteristic name of convexa. 



Crepidula aculeata Gmelin, var. costata Morton. 

 Patella aculeata Gmelin, Syst. Nat., p. 3693, 1788. 

 C. costata Morton, Journ. Acad. Nat. Sci. Phila. vi. p. 115, pi. 7, figs. 2, 3, 1829 ; Tuomey 



and Holmes, Pleioc. Fos. S. Car., pi. 25, fig. 11, 1S57. 

 C. spinosa Conrad, Proc. Acad. Nat. Sci. Phila. i. p. 377, 1S43 ; Medial Tert., p. 81, pi. 45, 



fig. 8, Tuomey and Holmes, Pleioc. Fos. S. C, pi. 25, fig. 10, 1857. 

 Crepidula aculeata Dall, Bull. U. S. Nat. Mus. No. 37, p. 152, 1889. 



Fossil in the Newer Miocene of the Chesapeake formation in Maryland, 

 Virginia, North and South Carolina and in the upper bed at Alum Bluff, 

 Florida, The typical form, aculeata, appears in the Floridian Pliocene at De 

 Leon Springs on the Caloosahatchie, Shell Creek and Alligator Creek, Dall 

 and Willcox; living from latitude 35° N . to latitude 35° S. on the eastern 

 shores of both Americas and eastward to Mauritius ; from low-water mark 

 to 589 fathoms (Blake Exp.). 



The distinction between the Miocene C. costata and the recent spinosa is 

 merely one of size and depth. The same variations in sculpture occur in 

 both ; the evenly striated, flattish Miocene specimens'are the typical costata ; 

 spinosa was founded on a specimen in which the radiating riblets were some- 

 what alternated, with the larger ones spinose; in other specimens all are spi- 

 nose. The alternated, partly spinose type is the most common both in the 

 fossil and recent shells. None of the smaller specimens of the Miocene 

 shells and none at all of the Pliocene specimens can be separated by valid 

 characters from the recent C. aculeata. . The type is represented on the 

 Pacific coast by the somewhat degenerate but very similar C. lingnlata Brod., 

 which is found there from the Pliocene to the recent fauna. 



