450 



NORTH AMERICAN INDEX FOSSILS. 



235. P. sinuosa Hall. (Fig. 591, d.) Devonic. 

 Extremities of hinge angular. Anterior portion of shell with 



broad sinus. Surface marked by fine undulating rays, crossed by 

 concentric striae which are at times crowded into lamellae. 

 Chemung : Pennsylvania. 



236. P. sao Hall. (Fig. 591, e,f.) Devonic. 

 Differs from P. sinuosa in the less distance between the anterior 



end of the shell and the sinus, and in the longer and more truncate 

 posterior wing. 



Chemung Group : New York. 



LXXII. Monopteria Meek and Worthen. 

 Differs from Pterinea in the absence of teeth, in the very obscure 

 or obsolete anterior muscle impression ; anterior ear represented 



Fig. 593. Monopteria longispina. (Kan. Pal., VI/II. ) 



Fig. 594. «, Monopteria gibbosa, right valve ; b, Pseudomonotis curia, left valve. 

 (Ind. Surv. and Kan. Univ. Quarterly.) 



by a very small appendage drawn back between the beaks in a 

 deep lunule, not seen in side view. Posterior wing slender, pro- 

 duced. Body of shell obliquely produced and angular posteriorly. 

 Devonic to Carbonic. 



237. M. longispina (Cox). (Fig. 593.) Carbonic. 

 Surface covered with fine concentric growth lines. 

 Kentucky-Colorado. 



238. M. gibbosa Meek and Worthen. (Fig. 594, a.) Carbonic. 

 Semicircular in antero-basal marginal outline, posterior end and 



wing about equally produced. 

 Pennsylvania-Kansas. 



LXXIII. Pseudomonotis Beyrich. 

 Suborbicular, inequivalve. Right valve convex, with prominent 

 incurved beak and small or obsolescent ears. Left valve flattened, 



