340 



NORTH AMERICAN INDEX FOSSILS. 



380. R. perplexa (McChesney). (Fig. 434.) Carbonic. 



Small ; moderately gibbous. Beaks prominent and incurved. 

 Pedicle valve without pronounced mesiaPsinus, but slightly flat- 

 tened or with a shallow though sharp depression anteriorly. Sur- 

 face marked by numerous very faint radiating lines and somewhat 

 stronger concentric lines, the latterlfinely crenulate, marking the 

 bases of hair-like spines not preserved. 



Widely distributed in North America. 



FlG. 434. Retiadaria perplexa (Ind. Geol. Survey). 



CV. Martinia McCoy. 

 Like Spirifcr,bu\: with hinge line shorter than the greatest width 

 of the shell, and cardinal angles obtusely rounded. Surface smooth 

 except for the concentric striae. Muscular impressions narrow and 

 faint. Devonic-Carbonic. 



Devonic. 



(Fig. 



435, a-b.) 



381. M. maia (Billings). 



Longitudinally ovate. Cardinal area narrow and sometimes 

 hidden bv the beak. Brachial valve with rounded mesial fold. 



c b 



Fig. 435. n-l>, Martinia maia ; c, Reticularis nevadaensis. ( After Walcott). 



Pedicle valve mure convex than the brachial, with a large in- 

 curved beak. 



Onondaga of Ohio, Nevada, Ontario. 



382. M. glabra (Martin). Carbonic. 



Subcircular to ovate. Pedicle valve with a moderately devel- 

 oped mesial sinus, high cardinal area and incurved beak. In the 



