CEPHALOPODA. 
229 
grit are chiefly made up from the results of many years’ collections in the 
Helclerberg mountains, and at Schoharie, for the State Museum. The few 
specimens in which surface characters are preserved will at once be apparent, 
while the otherwise imperfect condition of the greater number will sufficiently 
explain the difficulty of presenting a satisfactory monograph of the species. 
In the limestone coming above the Schoharie grit we have few species, and 
comparatively few individuals, of the genus; and these, so far as known to 
the writer, are in an imperfect condition, though often presenting the surface- 
markings. All the collections made from the limestones within the limits of 
the State of New York number less than fifty individuals. This fact may 
seem remarkable, when it is known that several species of Gyroceras attain 
their maximum development in the same horizon. 
At the base of the Hamilton group, the Marcellus shale affords six species 
of the genus, associated with Nautilus and Goniatites. In the mass of the 
same group, in a higher position, we have at least twenty species, some of 
which are extremely numerous in individuals. At the present time, however, 
we must regard this group of shales and shaly sandstones as not sufficiently 
explored to enable us to present a full account of its Cephalopodous fauna. 
In the Portage group the species and individuals yet known are not numerous, 
though it is quite probable that, in favorable localities, additional species will 
be found. The Chemung group has afforded few species, and these are frag¬ 
mentary, and in an unsatisfactory condition of preservation. 
In comparing the Orthoceratites of the New York strata with those of 
Bohemia, so amply and beautifully illustrated by M. Barrande, we find that 
the surface-markings in the latter are almost universally imbricating lamellose 
striae. Corresponding American forms have generally a reticulate surface. 
The curved forms, of which there are many in Bohemia, are very imperfectly 
represented among the American species. The “ brevicones” of Barrande, are 
scarcely known among the Orthoceratites of America, unless they may have 
been confounded with Gomphoceras. 
The annulated forms in Bohemia are usually marked with imbricating 
lamellae or lamellose striae, while in America many of the Lower Silurian 
