358 
PALEONTOLOGY OP NEW-YORK. 
The specimens originally referred to this species occur in the Genesee slate, 
and are more or less compressed or otherwise crushed, so that the real form and 
proportions cannot well be determined. The shell in this rock has been extremely 
thin, and the incipient plications outside of the mesial fold and sinus are usually 
almost obliterated by the pressure which has flattened the shell. In the compari¬ 
son of a considerable number of specimens from the black shale with those of the 
bluish shales of the Hamilton group below, I am somew T hat doubtful as to the 
propriety of separating the L. multicosta from this species, since in that one there 
is a great variation in the strength of the lateral plications, as well as in the space • 
tow r ards the cardino-lateral margins where they are more or less obsolescent. 
The cast of the interior shows an elongate narrowly ovate muscular area in the 
ventral valve, and a strong septum in the dorsal valve, which is^divided above and 
margined on each side by the muscular imprint. The entire interior of the shell 
or cast, when preserved, is beautifully marked by the ramifying vascular impres¬ 
sions which enclose the papillose ovarian spaces. 
The illustrations show the characteristic features of the species, as occurring 
in the Genesee slate. The ordinary size of specimens is from three-fourths to one 
inch in length, with a width nearly the same or a little greater. One specimen 
measures more than an inch and a quarter in length and an inch and a half in 
width. 
Geological formation and localities. This shell occurs in the Genesee slate at 
Bigstream point and other places on Seneca lake ; near Ogden’s ferry on Cayuga 
lake, and at other places thence to Ludlowville ; below Ithaca and elsewhere in 
the region of Seneca and Cayuga lakes. 
Leloihynchus multicosta. 
PLATE LVI. 
Leiorhynchus multicosta : Hall. Thirteenth Report on the State Cabinet, p. 85. °1880. ' 
Rhynchonella ? laura : Billings, Canadian Journal, No. xxvii, p. 273. 1860. 
Compare Leiorhynchus quadricostata (loc. cit.), ut sup. 
Shell ovate, with the length and greatest width nearly equal (in com¬ 
pressed specimens the width is often greater than the length); sides 
gently curving from the beak for about two-thirds the length, thence 
curving abruptly to the front, which is truncate in the middle for the 
width of the sinus. 
Ventral valve gibbous on the umbo, curving to the sides, becoming 
gradually depressed in the centre and forming a sinus which is broad 
