THE DEVONIAN FOSSILS OF CANADA WEST. 333 
ata and 8. ampla, showing clearly the inside of the area of the, ven- 
tral valve, and there are no such processes as those mentioned by 
Prof. Hall. It is also evident that if the Divaricator processes were 
as he says—articulated to processes beneath the area of the ventral 
valve—the shell could not be opened at all. The notch and groove 
in the Divaricator levers are simply the scars or marks of the attach- 
ment of the muscle. 
The divaricator processes 7. e. the (“ cardinal process bifurcate 
from the base’’) occur in all species of Strophomena, and are not 
peculiar to those which he has placed in his genus Strophodonta. 
They vary a good deal in their form in different species. The most 
ancient species in which I have seen them is S. filitewta. The fol- 
lowing Fig. 106 represents their form in this species, and it will be 
seen that they differ only specifically from those of S. demissa. 
Fig. 106. Fig. 107. 
Fig. 106. S.filiterta. a Divaricator processes, front view. 6 Viewed from the outside, 
shewing the groove. The specimen is from the Black River Limestone. s. The dental 
sockets. 
Fig. 107. 8. demissa. Copied from Geology of Iowa, Pl. 3, fig.5. c—Divaricator processes, 
front view. d—The same viewed from the outside. 
The specimen of S. jilitexta, from which the above fig. 106 was 
drawn, does not show the occlusor muscular scars, and in fact the 
interior of the dorsal valve is rarely so preserved as to shew them. 
In S. rhomboidalis and S. Philomela, the divaricator processes 
consist of two short ridges, abruptly terminated on the side of the 
area, their extremities not elevated above the surface of the shell, and 
if the length of the processes were of generic importance, then these 
two species would belong to a genus distinct from S. filitezta and 
S. demissa. 
As to the muscular impressions, the following figures will show that, 
although they are subject to considerable modifications of form, their 
arrangement does not vary. 
