262 
PALEONTOLOGY OF NEW YORK. 
This species is somewhat intermediate to M. Chemungensis and M. regularis, 
but is distinguished from the former by its shorter form, and from the latter 
by its greater convexity and more attenuate beak. This form and the suc¬ 
ceeding, were referred to Mytilops, but a careful comparison shows them to be 
related to the species here arranged under Mytilarca. 
Formation and locality. In the sandstones of the Chemung group, west of 
Smethport, Pa. 
Mytilarca gibbosa, n. sp. 
PLATE XXXIII, FIG. 20 ; and PLATE LXXXVII, FIG. 7. 
Shell of medium size; body ovate-arcuate, obliquely truncate along the hinge¬ 
line ; length less than twice the height; ventral margin nearly straight for 
more than three-fourths the length, abruptly curving into the posterior 
margin, thence gently rounded to the extremity of the hinge-line. 
Left valve very convex; the greatest convexity above the middle. 
Umbonal region gibbous. Right valve unknown. 
Hinge-line oblique, nearly equal to the height of the shell. Beak small, 
appressed, arching toward the ventral side. 
Test marked by fine concentric striae, which, at irregular intervals, are 
crowded into fascicles, leaving varices upon the surface of the cast. 
Interior unknown. 
The specimen described has a length of 45 mm., and height 26 mm. 
This species is proportionally longer, beak more acute, and much more * 
gibbous than M. lata. 
Formation and locality. In the Upper Chemung group, Napoli, Cattaraugus 
county, N. Y. 
Mytilarca lata. 
PLATE XXXIII, FIG. 22. 
Mytilops (Modiola) lata. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 33, fig\ 22 Jan., 1883. 
Shell large; body broadly sub-elliptical, abruptly narrowing toward the beak 
on the dorsal side; length one-third greater than the height; byssal area 
