264 THE DEVONIAN FOSSILS OF CANADA WEST. 
Genus AtryPA.—(Dalman.) 
SprriGERINA.—D Orbigny. 
Generic characters.—Shell circular, ovate or sub-quadrate. Ven- 
tral valve with a small closely incurved or sometimes elevated beak. 
Surface smooth, striated, or with small ribs, and often strongly 
marked with concentric squamose lines of growth. Shell structure 
fibrous, impunctate. The spiral appendages are placed with their 
bases flat upon the inner surface of the ventral valve, and their apices 
directed into the hollow of the dorsal valve. In the interior of the 
ventral valve, the divaricator muscular scars occupy a large oval 
space in the upper half; the occlusor a much smaller circular or oval 
space near the beak, and inserted, as it were, between the others on 
rostral side In the dorsal valve the occlusors are four in number 
near the beak, two on each side of an obscure median ridge. 
In fig. 83, a specimen of A. reticu- 
laris is represented lying on the ventral 
valve, the dorsal valve uppermost, shew- 
ing the position of the internal spires. 
The figure is taken from “ Sandberger’s 
Atlas.”’ 
ATRYPA RETICULARIS.—(Linn. ) 
ATRYPA RETICULARIS.—Of the generality of Authors. 
ATRYPA IMPRESSA.—Hall, Tenth Annual Report of the Regents of 
the University of New York, p. 122. 
sso 
Fig. 84. Fig. 85. Fig. 86. Fig. 87. 
Fig. 84.—Atrypa reticularis.—Dorsal view. Fig. 85.—Side view. 
Figs, 86 and §7.—A specimen with coarse ribs, 
Description.—This species is variable in form (as are all that range 
through a number of formations). Specimens the size of those above 
figured are ovate; length a little greater than the breadth ; sometimes 
both valves nearly equally convex, but in general the ventral valve is 
convex in the middle portion of the upper two-thirds, flattened to- 
