120 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



In Crassatellina, however, the only anterior lateral tooth yet made out 

 corresponds in position to the upper part of that in Etea, but is proportionally 

 much larger and longer, and extends back so as to connect with the upper 

 end of the anterior cardinal tooth. The posterior lateral tooth in Crassatellina 

 is also apparently more prolonged backward than in Mr. Conrad's genus. In 

 all other characters of the hinge these types agree exactly, and I am not quite 

 sure that some of these differences may not be rather apparent than real, 

 because, as already intimated, the specimens of Crassatellina yet examined 

 are merely casts, that may not convey an entirely correct idea of the details 

 of the hinge-teeth. I should also add that these shells likewise agree well 

 in their muscular and pallial impressions, as well as in the obscure traces of 

 radiating striae of the interior. Mr. Conrad thought the pallial line in his 

 type, sometimes a little truncated, or possibly very faintly sinuous; but in the 

 specimens that I have examined, it is well-defined, and clearly neither trun- 

 cated nor in the slightest degree properly sinuous. It extends backward and 

 downward, from near the middle of the under side of the posterior muscular 

 scar, nearly as far as the hinder margin of the same, and then curves abruptly 

 forward, thus leaving, as it were, a little notch between it and the muscular 

 impression above ; but this can hardly be viewed as a sinus of the pallial line 

 itself. 



Mr. Conrad's type has even more the external appearance of a Crassa- 

 tella than our shell, and I can no longer doubt that these shells, whatever 

 may be their generic relations to each other, really belong to the family 

 Crassatellidce. 



In regard to the geological range of this genus we only know that the 

 type was found in the Upper Cretaceous, at a horizon not far from that of 

 the Gray Chalk of English geologists. 



Crassatellina oblong a, Meek. 



Plate 2, rigs. 3, a, i, c, <1, e. 



Crassatellina oblonga, Meek (1871), Haydeu's Second Ann. Report Geological Survey of the Territories, 

 301, with cuts A and B. 



Shell small, short oblong-subtrapezoidal in outline, less than twice as 

 long as high; valves rather distinctly convex, with flattened sides; anterior 

 margin rounded; pallial margin nearly straight, or sometimes slightly sinuous 

 along the middle; posterior obliquely truncated above and narrowly rounded 



