TRANSACTIONS OF WAGNER 



574 



TERTIARY FAUNA OF FLORIDA 



Subgenus NUCULA s. s. 



The Neocene species of Nucida are quite puzzling, owing to the close 

 similarity of all the species in a general way, and the variability of each in 

 minor details. 



Nucula proxima Say. 



Nucula proxima Say, Journ. Acad. Nat. Sci. Phila., ist Ser., ii., p. 270, 1822 ; Tuomey 

 and Holmes, Pleiocene Fos. S. Car., p. 53, pi. 17, figs. 7-9, 1S55 ; Emmons, Geol. 

 N. Car., p. 287, fig. 208 B, 1858 ; Dall, Bull. 37, U. S. Nat. Mus., p. 42, pi. 56, fig. 4. 



Nucula obliqua Say, Am. Journ. Sci., ii., p. 40, 1820 ; not Lam., 1819. 



Older Miocene of New Jersey at Shiloh and Jericho, Burns ; Yorktown 

 beds of Virginia, Harris; north end of the Dismal Swamp, Virginia, Shaler; 

 Pliocene of the Caloosahatchie and Shell Creek, Florida, Willcox and Dall ; 

 Pleistocene of Simmons Bluff, South Carolina, Burns ; recent : (typical form) 

 from Charlotte Harbor, Florida, northward to North Carolina in two to one 

 hundred fathoms; (var. trunculus Dall) from Long Island Sound northward to 

 Nova Scotia. 



If a geographical series of this species be examined, it will be noticed 

 that the northern specimens are almost smoothly truncate behind, the es- 

 cutcheon is not impressed to any marked degree, and there is no angle at the 

 margin below the escutcheon. On the other hand, the specimens from the 

 southern coast, whence Say's type was derived, have a thinner shell with an 

 impressed escutcheon, the middle of which pouts more or less strongly ; the 

 valve-margin below the escutcheon has a projecting angle; the shell is some- 

 what compressed, compared with the northern form, and has a paler and more 

 delicate epidermis. Several of these characters are correlatives of the latitude, 

 but the extreme forms without a connecting series would be taken by any 

 careful observer for distinct species. Most of the conchologists of the United 

 States having resided north of Delaware, the northern form is the more 

 familiar both in books and collections, but it is not the original type, and I 

 have therefore given it a varietal name. The fossils, so far as yet observed, 

 are all more like the variety trunculus, corresponding to the cooler temperature 

 of the sea in this region during Miocene times, while the Pliocene specimens 

 are rather undersized, which may have been the result of the increasing 

 temperature which characterized that epoch in Florida. 



There is little doubt that the original Nucula obliqua of Say, from the 

 Miocene of Petersburg, Virginia, was a variety of N. proxima ; at any rate, the 



