TRANSACTIONS OF WAGNER 

 6i6 



TERTIARY FAUNA OF FLORIDA 



P. qtmiquer7igatus Conr., Am! Joiirn. Sci., xli,, p. 346, 1841 ; Med. Teit., p. 63, pi. 34, 



fig. 3, 1845 ; Tiiomey and Holmes, Pleioc. Fos. S. Car., p. 49, pi. 17, fig. 4, 1857. 

 P. wtdiitus Dall, Bull. Mus. Comp. ZooL, xii., No. 6, 238, 1886, c.x parte. 



Miocene of Jericho, New Jersey ; of Calvert and Charles Counties, Mary- 

 land ; Prince George and Dinwiddie Counties, the banks of the Nansemond 

 River near Suffolk, and on the York River, and Petersburg, Virginia; Wil- 

 mington and Cape Fear, North Carolina; Pliocene of the Waccamaw beds, 

 South Carolina, and of the marls of the Caloosahatchie, Florida; living on 

 the southeastern coast of the United States, in fifteen to sixty-five fathoms, 

 from Cape Hatteras to the West Indies. 



When I wrote my report on the Blake Pelecypoda, I had not had an 

 opportunity of studying well preserved G. pennacea, and was in doubt as to 

 its relations. I also accepted the traditional identifications of the names given 

 by Linnaeus, Lamarck, and other early writers to our American species. It 

 would seem that several of these names can never be absolutely determined, 

 and in the present synonymy I have dropped them and adopted the earliest 

 name which unmistakably refers to our shells. 



The unusually long synonymy which the present species possesses arises 

 from two causes, — carelessness and ignorance of the changes due to age. 



The large Glycymeris has two sorts of modifications, — one which is due 

 to variation, and the other correlated with growth and senility. 



In the very young shell the surface sculpture is always sparser, more un- 

 even, and sharper; in the adolescent specimen the ribs are usually well 

 marked and extend clear to the base ; the teeth are delicate and not inter- • 

 rupted by an invasion of the cardinal area. In the adult this invasion begins, 

 but otherwise the hinge is normal, the ribbing begins to become obscure dis- 

 tally, and the cardinal area enlarges. In the senile shell the cardinal area is 

 very large, only the ends of the arch of teeth remain, and these teeth are 

 usually enlarged; the concentric sculpture, due to intermittent instead of 

 steady marginal growth, becomes conspicuous. 



Individuals vary in regard to strength of sculpture and its lateral exten- 

 sion ; the two ends of the shell are rarely as clearly ribbed as the middle, and 

 sometimes have no ribs. The size of the hinge-teeth varies considerably be- 

 tween different specimens of the same size of shell ; in general a larger car- 

 dinal area and greater expansion of the valves near the hinge-line is correlated 

 with larger teeth. Specimens differ in amount of inflation and in outline 

 from nearly circular to transversely oval, and even sometimes a little oblique. 



