BRA CHIOPODA—NEO TREMA TA . 



199 



33. L. galenaense Winchell and Schuchert. (Fig. 233.) Ordovicic. 



Large, oblong, with nearly straight lateral and anterior margins. 

 Both valves strongly convex. Surface marked with concentric 

 striae which at irregular intervals rise into small pustules. 



Galena of Iowa, Wisconsin, Minnesota. 



NEOTREMATA. 

 XI. Acrotreta Kutorga. 

 Pedicle valve subcorneal with apex truncated by pedicle opening. 

 Posterior margin flattened, triangular and resembling a true cardi- 

 nal area ; this slope is divided medially by a shallow groove 

 widening downward. Brachial valve usually flat. Surface con- 

 centrically striated. Differs from Acrothele in having the slope 

 from the apex to the posterior margin vertical. Cambric. 



Fig. 234. a-c, Acrotretra gemma, side and summit view of ventral valve, and 

 dorsal valve, all X 3 '■> d> e i Acrothele subsidua, interior of dorsal and exterior of 

 ventral valves, X 3 > /> £> Acrothele matthewi, interior, exterior and profile views, 

 X 2 ; h, Iphidea bella ; *", J, Iphidea sivantonensis, ventral valve and profile, dorsal 

 valve, (/and^ after Matthew, the others after Walcott. ) 



34. A. gemma Billings. (Fig. 234, a-c.) Lower to Upper Cambric. 



Minute. Brachial valve circular and nearly flat with beak not 

 projecting beyond the hinge line and with wide, shallow mesial 

 sinus. Pedicle valve acutely conical with flat triangular area 

 whose base forms half the width of the shell. 



Montana, Utah, Nevada, Newfoundland. 



