268 THE DEVONIAN FOSSILS OF CANADA WEST. 
Fig. 92. 
Fig. 91. 
Fig. 91. Stricklandia elongata.—(Yanuxem.) Dorsal view of a specimen of a more nearly 
oval shape than usual. 
Fig. 92. The same, interior of ventral valve, shewing the small triangular chamber beueath 
the beak. 
and compressed towards the front; the ventral valve in general the 
most convex, obtusely carinated from the beak along the middle in 
the upper half; the dorsal valve in the upper half often much flattened 
and broadly carinated in the middle, sometimes evenly convex. In 
many specimens the sides are abruptly compressed, so that a transyerse 
section through both valves would be somewhat hexagonal in outline. 
The beak of the ventral valve is closely incurved over the umbo of 
the dorsal valve. Surface smooth but usually with several rough 
concentric imbricating ridges of growth most strongly developed 
towards the front. 
Length from two to three or even four inches; width from one 
half to two-thirds of the length. 
This appears to me to be a variable species, many of the specimens 
being somewhat broadly-oval, while others are elongate-oval or sub- 
cylindrical. So great are these differences that, without the interme- 
diate forms, the extremes might readily be classified as distinct species. 
The specimens are seldom found perfect. 
