356 Ei. Billings—New Species of Paleozoic Fossils, 
Generic Characters.—Shell unarticulated, ovate or sub-orbie- ! 
ular, lenticular, smooth, concentrically or radiately striated, 
sometimes reticulated by both radiate and concentric ste, 
Ventral valve with a solid beak and a small more or less dis 
tinctly grooved area. In the interior of the ventral valve there , 
are two elongated sub-linear or petaloid muscular im 
which extend from near the hinge line forward, sometimes to | 
points in front of the mid-length of the shell. These are either 
straight or curved, parallel with each other or diverging towanl 
the front. Between these, about the middle of the shell, isa 
median lin 
3 
two large ones dd. Should this be the case, however, the “a 
difference in their position would no doubt be of generic Vi 
P . Ae ie 
description of the dorsal valve of the 0. Apollinis suficiaty 
perfect to afford a means of comparison with that of a 
but the differences in the ventral valve alone are so 
closely related, and occur in nearly the same geologica 
] horizon. | 
In the rocks below Quebec and at the Straits of Belle Isle, 8 
vol. i, p. 292, pl. 80, fig. 2. Occurs at Troy, N. 
2. O. crassa 
Hall, = Orbicula ? crassa, op. cit. Pp. 299, ae 
fig. 8. Occurs at Troy. 
ne itudinal occupe le ME 
of the adductors, he says: pedro a Pee Rossies, 
__ * Speaking 
des = impressions et arrive jusqu’au sillon 
. 925 
i, p. 
