1 95 



Fig 98. Stropheodonta demissa. Ventral and dorsal views ; interior of pedicle and 

 brachial valves ; ventral, dorsal and lateral views of a large specimen (from Hall). 



Demissa bed, Sections 5, 6, etc. (abundant); eighteen inches 

 below the Encrinal limestone, at Section 6 (two specimens). 



Stropheodonta co ncav a. Hall. (Fig. 99.) (Pal. N. Y., 

 Vol. IV, p. 96, PL XVI.) 



Distinguishing Characters. — Large size; great convexity 

 of pedicle valve; high areas almost at right angles to each 

 other; surface of pedicle valve bearing coarse, sharp, crenu- 

 lated stria?, with commonly one or two between, which are less 

 elevated ; surface of brachial valve bearing distant strong- 

 stria?, with a number of finer ones between, all crenulated bv 

 concentric striae; large, spreading divaricator muscular im- 

 pressions occur in the pedicle valve; in the brachial valve the 



