260 THE DEVONIAN FOSSILS OF CANADA WEST. 
The specimens vary in form from oval (those with a short hinge- 
line) to sub-quadrate or sub-semicireular. 
This species is easily recognized even in fragments by its large 
rounded ribs.) When partially exfoliated the ribs sometimes exhibit 
from one to three large rounded knobby prominences. In general, 
however, they are smooth. 
Locality and Formation.—Near Port Colborne, and various places 
in the County of Haldimand. 
Collectors.—A. Murray, J. DeCew, E. DeCew, E. Billings. 
SPIRIFERA GREGARIA.—(Clapp.) 
SPIRIFER GREGARIA.—Hall. Tenth Annual Report of the Regents 
of the University of New York, p. 127, 1857. 
Fig. 74. Fig. 75. Fig. 76. 
Fig. 74. Spirifera gregaria.—Dorsal view. Fig. 75. The same.—Side view. 
Fig. 76. Ventral view. 
Description.—Shell semi-oval or sub-globular, varying greatly in 
the amount-of the convexity. Hinge-line straight, equal to the 
greatest width of the shell; cardinal angles sometimes rounded. 
Ventral valve very convex, strongly and uniformly arched from beak 
to front, the outline sometimes forming a semi-circle ; a deep angular 
mesial sinus extending from the front to the beak, on each side of 
which there are from seven to nine ribs. Umbo very much elevated, 
beak strongly incurved ; area concave, next to the hinge-line inclining 
outwards at an angle of.45° to the plane of the lateral margin, but 
above suddenly arched over the hinge-line by the strong incurvation 
of the beak. Dorsal valve convex, with a strong mesial fold either 
somewhat angular or a little flattened along the ridge, or obscurely 
marked with an indistinct groove; seven to nine ribs on each side 
surface, often nearly smooth but sometimes marked with concentric 
zigzag lines. Width about three-fourths of an inch; length varying 
from a little less to a little more than the width. 
In very convex specimens the umbo of the ventral valve is so 
