ORISKANY SANDSTONE. 
423 
Surface marked by from five to seven or eight plications on each side of 
the mesial fold and sinus, which are either round or subangular and 
more or less elevated. The entire surface is ornamented by fine closely 
arranged concentric strias ; and these are again crossed by finer ra¬ 
diating strise, which are more prominent on the edges of the lamellae, 
giving to the perfect shell a granulose exterior. 
The casts of the ventral valve, which are abundant in the sandstone, 
show a large prominent process which is strongly defined by the impres¬ 
sions of the dental lamellae : this process, which indicates the form and 
dimensions of the muscular area, is variously striated, sometimes with a 
few strong ridges, and in others with finer longitudinal striae, and more 
rarely the curving transverse striae are preserved. The cast is strongly 
papillose on each side of the muscular area. The cast of the dorsal valve 
shows a sharp median line down the fold, indicating the interior median 
ridge. 
This shell is very variable in its original form and proportions, and in the greater 
or less angularity of the plications. The finer surface markings are rarely preserved 
in the sandstone, and the fossil is found in various degrees of exfoliation, from 
specimens preserving the greater part of the shell, to those which are complete casts 
of the interior. It has likewise suffered more or less from distortion, so that it ap¬ 
pears under various aspects, and might be mistaken in its different phases for more 
than a single species. 
This fossil has been referred by M. de Verneuil to the Spirifer macropterus of 
RcEfaER*, to the casts of which it bears some resemblance. In our shell the hinge is 
never so extended, nor the plications so numerous; the area is wider, and never so 
linear as in the European species; and though in its numerous variations the casts 
of our species offer some analogy with the figure of Dr. Rcemer, the muscular im¬ 
pression is always more prominent, showing originally a more elevated beak. While 
no specimen of the shell observed offers a very great similarity to the figure 4 of 
the plate referred to, a specimen of our species, of the same extent of hinge-line, 
would present a beak of more than a quarter of an inch above the line of the dorsal 
valve. 
The Oriskany species bears a considerable similarity to some forms of Spirifer 
brought from the Falkland islands by Mr. Darwin, and described by Messrs. Morris 
C. F. Rcemkr : Das Rheiuisclie Uebergangsgebirge, pag. 71, tab. 1, f. 3 &.4. 
