446 DESCRIPTIONS OF NEW SPECIES OF FOSSILS FROM THE 



rays are crossed by fine, concentric, ci'ennlating stripe, which become fasciculated on 

 the anterior ear. IS^ear the base there are frequent concentric undulations. 



The specimen from which the description was made measures as follows : height 

 50 mm. ; width 50 mm. ; length of hinge line 35 mm. 



Formation and localitij. Chemung group, one mile north of Warren, Wai-ren 

 county, Pennsylvania. 



LYEIOPECTEN ALTERNATUS Simpson, n. sp., Fig. 12. 



Shell large, broadly ovate, nearly circular ; height about equal to the longitudinal 

 diameter ; basal and lateral margins i-egularly rounded. 



Left valve moderately convex ; greatest convexity above and a little anterior to 

 the middle, gradually sloping to the base, more abruptly curving to the cardinal and 

 "' '" " ■ - ' , antero-basal margins. 



/ Right valve unknown. 



irTT^^ i^jf Hinge line straight, length a little more 



; 1 than one-half the transverse diameter of the 



; \ \ valve. 



1^'//// Anterior ear short, triangular, not well de- 



• fined; posterior ear triangular, flat; limits not 

 /< v>l well defined except near the beak; margin 

 </, v./ slightly concave, nearly straight; extremity. 



v., V 1 



V • , ./ angular. 



X^: , ■ / ° 



X ; ', . •^'' Surface marked by more than thirty com- 



■^-, Va>^ 



APS Tr i?89 "*-*^ paratively strong, sharply rounded rays ; between 



adjacent prominent rays ai-e usually three smaller rays, the central one of which is 



larger than the others, occasionally nearly as prominent as the principal ones ; the 



other two are much finer. On and ne ir the posterior ear, and also near the anterior, 



this disposition is not conspicuous, the radii being more nearly of the same size. The 



radii are crossed by occasional lines of growth. .No concentric striae have been 



observed. 



This species somcvvliat resembles Lyrlopeden tricostatas of this formation, but 

 may be distinguished by its more nearly circular form, by the greater number of and 

 less prominent radii, antl the sti'oiiger central one of the three intermediate stri:e ; 

 from L. magnificns and L. mricrodontus by its smaller size and the decided difference 

 in the ornamentation of the surface. 



Formation and locality. Chemung group, one mile north of Warren, Warren 

 county, Pennsylvania. 



