BRACHIOPODA—PROTREMATA. 231 



112. S. inaequalis Hall. Mississippian. 

 Hinge line equalling the greatest width of the shell. Brachial 



valve very gibbous, with the greatest convexity near the center. 

 Pedicle valve nearly flat. Surface marked by alternating larger 

 and smaller radiating striae. 



Kinderhook of Pennsylvania, Ohio, Iowa, Utah. 



113. S. crenistria (Phillips ?). (Fig. 281, c-e.) Mississippian. 

 Wider than long, with hinge line slightly shorter than width of 



the shell below. Brachial valve convex medially, pedicle valve 

 flattened. Surface covered with numerous subequal or alternating 

 larger and smaller radiating striae, crossed by fine and crowded 

 concentric striae. Length of a rather large specimen 1^ inches 

 and breadth 2 inches. 



Ohio, Michigan, Nevada, Nova Scotia, Feilden Isthmus in lat. 

 82 , 43'. 



XXXIX. Orthotetes Fischer de Waldheim. 



{Derbya of authors generally.) 



In general like Schtichertella but the pedicle valve is at times 

 much elevated at the beak and is rarely concave. It differs dis- 

 tinctly from Schuchertella in the presence in the pedicle valve of a 

 high median septum extending longitudinally through the center 

 of the muscular area, which is one third to two thirds the length 

 of the valve. Carbonic. 



114. 0. (Derbya) keokuk Hall. (Fig. 281,/.) Mississippian. 

 Differs from 0. crassus in its broadly semielliptical outline and 



convexity of brachial valve which is often equal to one third the 

 width of the shell. 



Kinderhook-Keokuk of Iowa, Illinois, Indiana, Missouri, Nevada. 



115. 0. (Derbya) crassus (Meek and Hayden). (Fig. 282, a-d.) 



Upper Carbonic. 



Subquadrate, owing to the broadly rounded front and somewhat 

 straightened lateral margins. Pedicle valve nearly flat and usually 

 with a somewhat distorted beak. Brachial valve gently convex in 

 the middle. Surface marked by numerous raised radiating striae 

 crossed by concentric lines and stronger growth lamellae. Average 

 size about 1 inch in length and breadth. 



Widely distributed through central and western North America. 



