MARYLAND GEOLOGICAL SURVEY 649 



The genus originated, apparently, in the Cretaceous, culminated in the 

 Tertiary, and is represented in the Recent faunas by some thirty or forty 

 species confined, for the most part, to the tropical seas. In the East Coast 

 and Gulf Eocene, and in the East Coast Miocene, the genus is one of the 

 most prolific and conspicuous of any of the bivalves. 



A. Outline ovate or ovate-trigonal, not conspicuously produced along the 



posterior keel. 



1. External surface incrementally sculptured but not more or less 



regularly lineated from umbones to base. 



a. Shell very heavy, especially in the umbonal region; posterior 



carina usually prominent Crassatellites vadosus 



b. Shell not very heavy and uniform in weight; posterior carina 



not very prominent Crassatellites subplanus 



2. External surface more or less regularly lineated from umbones 



to base Crassatellites linteus 



B. Outline alate, conspicuously produced along the posterior keel. 



Crassatellites pteropsis 



CRASSATELLITES VADOSUS (Morton) Johnson 

 Plato XXXIX, Figs. 1-4 



Crassatella vadosa Morton, 1834, Syn. Org. Rem. Cret. Group, U. S., p. 66, 



pi. xiii, fig. 12. 

 Crassatella ripleyana Conrad, 1858, Jour. Acad. Nat. Sci., Phila., 2d ser., 



vol. iii, p. 327, pi. xxxv, fig. 3. 

 Crassatella vadosa Meek, 1864, Check List Inv. Foss., N. A., Cret. and Jur.. 



p. 11. 

 Crassatella vadosa Stoliczka, 1871, Mem. Geol. Survey of India, Pal. Indica, 



Cret. Faunas Southern India, vol. iii, p. 295. 



Crassatella vadosa Gabb, 1876, Proc. Acad. Nat. Sci., Phila., p. 310. 

 Crassatella vadosa Conrad, 1878, Cook's Geol. of New Jersey, p. 726. 

 Crassatella vadosa "Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 116. 



pi. xvii, figs. 12-15. 



Crassatellites vadosus Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 14. 

 Crassatellites ripleyana Johnson, 1905, Ibidem. 

 Crassatellites subplanus Weller, 1907, Geol. Survey of New Jersey, Pal., vol. 



iv, p. 553 (ex parte), pi. Ixi, figs. 1, 2(?). 



Description. " Ovato-triangular, slightly compressed ; with about 

 thirty distinct, concentric stria?. Length one inch and a quarter ; breadth 

 one inch." Morton, 1834. 



Type Locality. Prairie Bluff, Alabama. 



Shell of medium size, thick, heavy, rudely trigonal in outline; anterior 

 and lateral margins rounded, posterior more or less produced and trun- 



