PELECYPODA—PRIONODESMACEA. 



441 



I /y . Greatest length subparallel to hinge line. 



209. /. simpsoni. 

 I // '. Greatest length at about 45 ° to hinge line. 



214. /. labiatus. 

 bb. Beak but little in advance of middle of shell. 



219. /. vanuxemi. 



Cretacic. 



208. I. dimidius White. (Fig. 579.) 

 Shell small. Beaks pointed, small, 



but prominent. Valves subequal. 

 Coloradoan : Kansas, Colorado, 



Utah, New Mexico. 



209. I. simpsoni Meek. (Fig. 580.) 



Cretacic. Fig. 579* Inoceramus dimidius, 



T » 1 ,1 , . 1 left and anterior views. (After Stan- 

 Large ; length nearly twice the „ „ v 



a > » J ton, Bull. 106.) 



height. Anterior end very short. 



Beaks incurved, projecting but little above the hinge line. 



Fig. 580. Inoceramus simpsoni, right valve, XX* (^* S- G. S., Bull. 106.) 



Coloradoan : Kansas, South Dakota ; also Cretacic of San Luis 

 Potosi. 



210. I. fragilis Hall and Meek. (Fig. 581, a.) Cretacic. 



Anterior side vertically truncate. Beaks almost equal, pointed, 

 scarcely rising above the hinge line, curving inward and slightly 

 forward at the points. Surface marked with fine growth lines and 

 a few obscure concentric undulations. 



Benton : Texas to Dakota and Montana. 



