LAMELLIBRANCHIATA. 429 



PARARCA, N. G. 



[ Types P. transversa, P. veiiusta, P. Sao and P. erecta. ] 



PaRARCA PRiECEDENS. 



PLATE XCIV, FIG. 19. 



Shell of medium size, broad-ovate, narrowing posteriorly ; length one fourth 

 greater than the height; basal margin regularly curving. Posterior extrem- 

 ity rounded. Cardinal line straight and apparently slightly declining poste- 

 riorly. Anterior end declining rapidly from the beak and regularly rounded 

 below. 



Valves moderately convex below, becoming gibbous in the middle and 

 above. 



Beaks at about the anterior third, prominent. Post-umbonal slope prom- 

 inent, extending to the posterior extremity. 



Surface marked by numerous, fine rounded radii, with narrow interspaces. 



The specimen described has a length of 31 mm. and a height of 24 mm. 



This species diifers from P. neglecta in its larger size, more elevated beak and 

 finer striae ; the radii upon the anterior slope are notably much finer than in 

 that species. The species is described from a gutta-percha impression of the 

 natural mould. 



Formation and locality. In the cherty layers of the Corniferous limestone, in 

 Cayuga, Canada West. 



Pabarca transversa. 



PLATK LXX, FIGS. 12, U, 15. 



In part Cardiola transtersa. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 70, figs. 12-15. 



1883. 



Shell small, oblong, sub-elliptical; length about one-third greater than the 

 height ; basal margin regularly and gently curving. Posterior extremity 

 broadly rounded or somewhat obliquely sub-truncate. Cardinal line straight, 

 55 



