440 



NORTH AMERICAN INDEX FOSSILS. 



207. G. ensiformis (Conrad). (Fig. 578.) Cretacic. 



Very oblique, elongate, narrow, and somewhat sickle-shaped. 

 New Jersey (Merchantville-Red Bank), and Gulf region. 



FlG. 578. Gervilliopsis ensiformis, interior of left valve and basal view of anterior 

 end. (After Whitfield, Pal. N. J., I.) 



LXVII. Inoceramus Sowerby. 



Rounded, marked with more or less prominent concentric undu- 

 lations. Umbos prominent, somewhat anterior. Hinge line long, 

 straight, without teeth, but with numerous, small, transverse liga- 

 ment pits. Jurassic, Comanchic and especially Cretacic. 



A. Valves strongly unequal 213. I. umbonatus. 



B. Valves subequal I. 



I. A median depression in each valve 212. /. gilberti. 



I. No median depression I. 



I. Umbos thick, rather strongly elevated a. 



a. Concentric undulations angular 211. /. undabundus. 



a. Concentric undulations rounded.. 215. I. dcformis. 



I. Umbos low but often prominent b. 



b. Height of shell about I inch or less 208. /. dimidius. 



b. Height of shell 2 inches or more 11. 



II. Beak very acute aa % 



aa. Height about 1.5 inches 210. I. fragilis. 



aa. Height about 6 inches 216. /. altus. 



11. Beak rather obtuse bb. 



bb. Beak at anterior edge of shell 220. /. barabini. 



bb. Beak not quite at anterior edge of shell f. 



f . Average length of shell less than 3 inches. 



218. I. proximus. 



\. Average length of shell more than 3 inches *. 



*. Length and height about equal. 



217. /. nebrascensis. 

 *. Length greater than height.. i // . 



