232 NORTH AMERICAN INDEX FOSSILS. 



Fig. 282. a-d, Orthotetes crassus ; e-g, Meekella striatocoslata. (Ind. Geol. 

 Surv. ) 



XL. Meekella White and St. John. 



Very biconvex ; often subpyramidal ; surface plicated. Hinge 

 line straight, shorter than the greatest width of the shell. Cardinal 

 area of pedicle valve high, with deltidium which is convex in the 

 middle and flat along the sides. The prominent dental lamellae 

 are prolonged forward as septa for half the length of the shell. 

 Cardinal area of brachial valve linear; umbo gibbous; cardinal 

 process thin, erect and high, at times almost reaching the apex of 

 the umbonal cavity of the pedicle valve. Surface of valves, includ- 

 ing the coarse radiating plications, covered with fine radiating striae. 

 Upper Carbonic. 



116. M. striatocostata (Cox). (Fig. 282, e-g.) Upper Carbonic. 



Beak usually distorted by being flattened. Surface of both 

 valves marked by 10 to 14 angular plications, not extending to 

 the beak and separated by deep angular interspaces. The whole 

 surface covered with fine radiating striae which in maturity con- 

 verge upon the crests of the plications and meet one another. 



Distributed throughout the western United States. 



XLI. Hipparionyx Vanuxem. 

 Large, like Schuchertella but with a very convex brachial valve 

 which has no cardinal area ; cardinal process high and bifid. 

 Pedicle valve nearly flat, with low cardinal area. Teeth supported 



