344 THE DEVONIAN FOSSILS OF CANADA WEST, 
width of one line ; these are crossed by fine concentric strie eight to 
twelve in one line. The radiating striz increase both by subdivision 
and intercalation of new ones between the old; they are often irregu- 
larly undulated, and the surface of the shell has thus a somewhat 
minutely uneven surface. In some specimens, however, this charac- 
ter is not apparent. 
In the interior of the ventral valve the muscular impressions 
occupy a large sub-triangular depression in the substance of the shell. 
This is about a line wide at the hinge line, from which point the sides 
of the depressed space are nearly straight, and diverge outwards at an 
angle of about 45° to the median line of the shell. The depression 
gradually disappears, so that it is difficult to define its front margin. 
Still, in very well preserved specimens, it can be seen that the divari- 
cators are of an elongate oval shape, and that they extend more than 
half the length of the shell; the occlusors are elongate oval, and. 
situated close to the hinge line, their length one-third of that of the 
divaricators. These latter are sometimes divided into several lobes by 
thin, slightly elevated, longitudinal ridges. On each side of the mus- 
cular cavity, near the hinge, the shell is covered with small tubercles. 
This species is so easily recognized. by its flat form and evenly 
striated surface that a figure of it is unnecessary. 
Although it has received a separate name for every formation in 
which it occurs, yet I cannot make out the slightest difference 
between the specimens of the Oriskany Corniferous and Hamilton 
rocks. I think, also, that S. magnifica of Hall is only a large variety 
of this species. 
Locality and Formation.—Oriskany Sandstone, Corniferous Lime- 
stone, in County of Haldimand. Hamilton Shales, Township of 
Bosanquet. 
Collectors.—E. De Cew, J. De Cew, E. Billings. 
STROPHOMENA LEPIDA.—(Hall). 
SrropHODONTA LEPIDA.—(Hall). Geology of Iowa. Vol. 1., part 
2, p. 493. Pl. 3, figs. 3a, 30, 3c. 1858. 
Compare 8. nacrEa.—(Hall). Tenth Annual Report of the Regents 
of the New York University, p. 144, Also, S. tepis.—(Bronn). 
Lethea geognostica, 3rd edition. Vol. I., p. 367. Atlas. Pl. 2, 
figs. 7, a, b, c. 
Description.—Shell small, smooth or scaly, no radiating striz, 
about three-fourths of an inch wide, half an inch long, sub-semicir- 
