LAMELL1BRANCHIA TA. 
429 
PARARCA, n. g. 
[ Types P. transversa, P. venusta, P. Sao and P. erecta. ] 
Pararca PR^CEDENS. 
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 differs from P. negleda 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. 
Pararca transversa. 
PLATE LXX, FIGS. 12, 14, 15. 
In part Cardiola transversa, 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 
