BRA CHIOPODA—PROTREMA TA. 



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 Fig. 263. Strophcodonta demissa, ventral and dorsal views, X 



(After Hall.) 



Fig. 264. Slropheodonta (Leptostrophia) perplana, ventral view, and interior of 

 brachial valve. 



closed. Brachial valve very concave. Surface covered with strong, 

 sharply elevated radiating striae, each alternating with three or five 

 smaller ones. 



Chemung of New York, Iowa, Nevada, Manitoba. 



XXXIII. Pholidostrophia Hall and Clarke. 

 Differs from Stropheodonta in the smooth, often nacreous surface ; 

 marked only with a few squamose growth lines. The interior of 

 the brachial valve bears three 

 diverging ridges in front of the 

 muscle area. Devonic. 



87. P. iowaensis (Owen). (Fig. 



265.) .S. nacrea Hall. Fig. 265. Pholidostrophia iowaensis, 



Devonic dorsal, profile and ventral views, X *• 



.„..,, . (After Hall.) 

 Small, semielliptical, having 



a brilliantly nacreous lustre. Brachial valve concave; pedicle valve 

 convex. Beak small and depressed. Surface apparently smooth, 

 but crossed by microscopic growth lines. 



