BRACHIOPODA—ORTHIDJE. 



257 



180. 0. strophomenoides Hall. Devonic. 



Beak of pedicle valve but little elevated above the hinge line; 

 that of brachial valve somewhat the more prominent. Surface 

 marked by a distinct, narrow mesial elevation on the pedicle valve 

 from beak to front and by a corresponding depression on the 

 brachial valve. 



Helderbergian of New York, Maine, Tennessee, etc. 



LIII. Platystrophia King. 



Exterior spiriferoid but interior lacking the calcified brachidia of 

 Spitifer. Hinge line long and straight. Cardinal areas almost 

 equally developed on both valves, thus differing from Spirifer. 

 Both valves very convex, the brachial the more so, with a strong 

 median fold on the brachial valve and a corresponding deep sinus 



Fig. 308. a, b, Platystrophia crassa ; c, d, P. lynx, wax. (Minn. Geol. Surv. ) ; e-i, 

 P. acutilirata (Ind. Geol. Surv.). 



on the pedicle valve. Both valves marked by strong sharp pli- 

 cations which extend over sinus and fold. The teeth are thick and 

 very prominent. Ordovicic-Siluric. 



