LAMELLIB RANCHI A TA. 
191 
Left valve convex, gibbous above. Right valve depressed-convex below, 
and abruptly gibbous at the umbo. 
Hinge-line straight; length less than the length of the shell. 
Beaks sub-anterior, obtuse, erect, prominent, arching over the cardinal 
line. Umbonal region gibbous and gradually sloping down to the general 
convexity, abruptly limited on the posterior side, subtending an acute angle. 
Anterior end extended, acute and nasute. Wing large, triangular, slightly 
convex, joining the body of the shell more than two-thirds of the length 
below the beak; margin symmetrically concave; extremity produced and 
very acute. In the right valve the anterior end is broad and flat; the wing 
is large, with no defined limit between it and the body of the valve. 
Surface marked by elevated concentric striae which, at irregular intervals 
are fasciculate, producing undulations on the surface. This character is often 
marked on the front of the shell where the fascicles are composed of three 
or four distinct striae. 
Interior unknowji. 
A specimen of the left valve has a length, measured from beak to base, of 
44 mm., height 30 mm., hinge-line about 38 mm. Another example has a 
length of 45 mm., height 25 mm., hinge-line 32 mm. A right valve measures 
43 mm. in extreme length, height 30 mm., hinge-line about 34 mm. 
This species bears some resemblance to L. robustum, but the body is more 
oblique and not so broad below; the anterior extremity is acute; the wing 
larger, more extended along the valve and very symmetrically concave on the 
margin. The form of the shell is very similar to L. longispinum, but differs 
by its larger wing, the broader sinus and more regularly rounded posterior 
extremity, and in the latter respect it resembles L. Shumardi, while it is 
otherwise very different. 
Formation and localities. In the Chemung group at Portville and Little 
Genesee, Alleghany county, N. Y. 
