CRANLE OF THE HAMILTON GROUP. 
29 
adhering shale, the appearance of the exterior of the small funnelshaped fronds 
of Fenestella. The strim are similar to those of Crania ( Pseudocrania ) divaricata 
of M'Coy, a Silurian fossil; but the form and position of apex is very distinctive. 
The ventral valve of this species has not yet been discovered, unless it may 
occur among the imperfect and obscure specimens which have been referred to 
C. hamiltonicR. 
Geological formation and locality. In shales of the Hamilton group : Alexander 
in Genesee county; on the shore of Canandaigua lake in Ontario county; and at 
Eighteen-mile creek on Lake Erie, N.Y. 
Crania gregaria (n. s.). 
PLATE III. 
Shell small, obliquely very depressed-conical,, subcircular or oblate, nar¬ 
rower at the posterior end; apex at the posterior third of the shell. 
Surface apparently smooth. 
This small species occurs from the size, of a pin’s head, to those having a 
transverse diameter of a little more than a tenth of an inch, with a longitudinal 
diameter a little less than one-tenth of an inch. On a single valve of a large 
bivalve shell, nearly forty individuals of this species can be seen, together with 
the remains of several ventral valves of one of the larger species. 
It may be possible that these small fossils are the young of C. hamiltonice , which 
have commenced their existence upon the same body which sustained the parent 
shells. 
Geological formation and locality. In the shales of the Hamilton group, in 
Bristol, Ontario county. 
