254 THE DEVONIAN FOSSILS OF CANADA WEST. 
This genus ranges from the Lower Silurian up to the Trias. In 
Canada we have found no species below the Clinton group. 
A great many species of this genus have been described as occurring 
in the Devonian rocks of the United States; and in Canada West 
there are apparently fifteen or twenty, but owing to the imperfection 
of the specimens, several of these must remain for a while undeter- 
mined. 
SPIRIFERA MUCRONATA.—(Conrad.) 
DELTHYRIS MUCRONATUS.—(Conrad.) Annual Report of the 
Geological Survey of New York, 1841, p. 54. Hall, Geology of 
New York, part 4, 1843, p. 198. 
: Fig. 62. 
Fig. 59 Spirifera mucronata.—Ventral view. Fig. 60. Side view. Fig. 61. Dorsal view. 
Fig. 62. A long-winged variety of the same species. 
Description.—This species varies from the semi-circular to the sub- 
triangular form. In general the hinge line is twice, and sometimes 
thrice the length of the shell; the cardinal angles acute, the side 
either straight or gently rounded and converging to the front margin, 
which is either straight or concave, and of the width of the mesial ” 
fold. The valves are moderately convex; the ventral more tumid 
than the dorsal; the mesial fold and sinus are rounded, and extend 
quite to the beaks; from fifteen to twenty not very prominent ribs on 
each sidee The area of the ventral valve is very narrow, in the 
largest specimens scarcely more than half a line in height ; the beak 
small, pointed and incurved over the area, but not in contact with. the 
