TRANSACTIONS OF WAGNER 

 1464 



TERTIARY FAUNA OF FLORIDA 



ligament internal. Fossarina Clessin (ex parte), not of Adams, is synony- 

 mous. 



Pisidium saginatuvi White, in Powell, " Geology of the Uinta Mountains," 

 p. 128, 1876, and P. contortiun Prime, " Annals Lyceum of Natural History 

 of New York," vi., p. 65, pi. i., fig. 2, 1853, are the only two exclusively fossil 

 species yet recorded from the United States. The former is from the upper 

 Cretaceous lignite beds of Evanston, Utah, and the latter from the Pleistocene 

 marl of Pittsfield, Massachusetts. A number of species have been reported 

 from the loess and freshwater marls of the Mississippi Valley and Eastern 

 States, which it is perhaps hardly worth while to enumerate here, but I may 

 note that P. virginicum Gmelin is known from the marls of the Yukon Valley, 

 Alaska, as well as from the existing fauna. 



Superfamily ASTARTACEA. 



Family CRASSATELLITID^. 



This group takes form in the upper Cretaceous. There are a number of 

 names applied to genera or groups supposed to belong to this assembly of 

 which material is not accessible to me sufficient to work out the origin and 

 development of this family or the validity and accuracy of the characters upon 

 which these minor groups are referred to it. I shall therefore confine my 

 attention in the main to the Tertiary forms which have been described from 

 American strata. A few Mesozoic types may be incidentally noticed. 



In Crassatellites, as in Mactra, the essential features of the family began 

 to crystallize in the middle and upper Cretaceous. Especially the descent of 

 the resilium and ligament then began, and we find in the Cretaceous Eriphyla 

 of Gabb the ligament still lingering externally, while in the Tertiary and recent 

 Crassinella this organ has followed the resilium to the interior and is wholly 

 cut off from the exterior. In the early Crassatellites the ligament and resilium, 

 though internal, are small and by no means cover the space on the broad hinge- 

 plate which they occupy in late Tertiary time. The posterior right cardinal 

 and the fossette for the posterior cardinal of the opposite valve are affected 

 by the pressure of the descending resilium and dwarfed by it, a condition which 

 was observed by Conrad in Crassatella vindinnensis Orbigny, of the French 

 Chalk, and upon which he founded his genus or subgenus Pachythcerus in 1869. 

 The same state of affairs is plainly visible in several of our Eocene species. 

 The nepionic shell of some Crassatellites, including the Eocene type of the 

 genus, is convex with a tendency to quadrangularity, while other species have 

 it flattened and elongate-ovate or trigonal. Upon a young shell of this de- 



