52 



[ Senate 



Steophomena ( Strophodonta) beckh ( n. s.). 



Pal. N.Y. Vol. iii, pi. 22, f. la - It. 



Shell subsemicircular or subquadrate ; lengtli sometimes equal to 

 the width ( tliough usually from two-thirds to three-fourths as 

 great) : ventral valve depressed - convex ; beak very small : 

 dorsal valve fiat or a little concave near the hinge, slightly 

 convex near the front : hinge-line crenulated, generally equal 

 to the greatest width of the shell, but sometimes less; area 

 linear, confined to the ventral valve ; foramen small, open or 

 closed. Surface marked with fine, regular, closely arranged, 

 bifurcating, radiating striee, crossed by fine obscure concentric 

 lines, and small more or less regular concentric wrinkles which 

 curve outwards on approaching the hinge. 



This species is very closely allied to Strophomena [Leptcsna) sowerhyi 

 of Barrande ( Sil. Brach. aus Bohmen, pi. 21, f. 1 & 2 a, b, c, e); but 

 differs from those figures in being more coarsely striate, with the concentric 



"g;^ \r 





Steophomena bbokii. 



