32 PROCEEDINGS OF THE ACADEMY OF [1887. 



ON NEW GENERIC FORMS OF CRETACEOUS MOLLUSCA AND THEIR 

 RELATION TO OTHER FORMS. 



BY CHARLES A. WHITE. 



Published by permission of the Director of the United States Geological Survey 



The type species of the three generic forms which are described 

 in this article ^ belong to the collections of Cretaceous fossils from 

 Texas, which I am now preparing for publication in one of the 

 memoirs of the U. S. Geological Survey. In their generic charac- 

 teristics all three of them apj^ear to be respectively identical with 

 certain forms Avhich have long been known, but which have been 

 referred to other genera by different authors. The features which 

 I now present as having generic value seem to have been overlooked 

 by those authors, or, so far as they were observed, they were treated 

 as specific characters. Two of these forms belong to the section 

 Melininse of the family Aviculidse. The other is referred to the 

 Crassatellidfe, but it departs considerably from the typical section 

 of that family. 



CRASSATELLIDiE. 



Genus STEARNSIA (gen. nov.). 



Shell compressed, subtrihedral or subcircular in marginal out- 

 line; beaks small, closely apjiroximate, prominent by reason of 

 the abrujjt sloping away of both the antero-and postero-dorsal 

 borders; lunule and escutcheon both well defined and flattened 

 or excavated; hinge strong, consisting of both cardinal and 

 lateral teeth; cardinal teeth two in the left valve and three in the 

 right; both posterior and anterior lateral teeth long aud slender; 

 posterior laterals two in the right valve and one in the left; 

 anterior laterals two in the left valve and one in the right. If, 

 however, the overlapping border of the right valve and the enter- 

 ing border of the left, within the lunule, and the overlapping 

 border of the left valve and the entering border of the right, 

 within the escutcheon, be regarded as teeth, the number of both 

 the anterior and posterior laterals is two in each valve; ligament 



^ The names under which I liave described these forms respectively are 

 Dallicoftcha, Stearnsia and AguiUria. They are given in honor of Dr. W. 

 H. Dall and Dr. R. E. C. Stearns of the U. S. Geological Survey, and of 

 Senor Jose G. Aguilera, of the Mexican Geographical and Exploring 

 Commission. 



