224 NORTH AMERICAN INDEX FOSSILS. 



Fig. 271. a-d, Strophomena incurvata, a, exterior of convex brachial valve ; b, 

 interior of pedicle valve ; c, interior of brachial valve ; d, profile ; e-f, Strophomena ru- 

 gosa, ventral and dorsal views ; g-h, Strophomena trilobata, dorsal and profile views; i-j, 

 Leptcena unicostata, exterior and profile views of ventral valve. All natural size, {e-f 

 after Indiana Geol. Surv. , the others after Winchell and Schuchert, Minn. Geo!. Surv. ) 



99. S. neglecta (James). (Fig. 272, b.) Ordovicic. 

 Of medium size, about one and one third inches wide by an inch 



in length with usually the greatest width at the hinge line. Sides 

 meet the hinge line about at a right angle. Surface covered with 

 fine, subequal radiating striae. 



Lorraine of Ohio, Indiana, Illinois, New Mexico. 



100. S. rugosa (Rafinesque MS.) Blainville. (Fig. 271, e-f.) 



Ordovicic. 

 Pedicle valve deeply concave, brachial evenly convex. Of 

 medium size with greatest width at the hinge line. Cardinal ex- 

 tremities somewhat acute. Surface covered with numerous fine 



