CEPHALOPODA. 
317 
tral diameters of 6.5 and 4.5 mm. at the two extremities. Other fragments 
have been observed, indicating but slight variations from these dimensions. 
This species closely resembles B. carinatus, Monster, as described and figured 
by the Drs. Sandberger in Verstein. des Rhein. Syst. in Nassau, except that it 
is larger, the carination on the dorsum (?) is less marked, and none of the 
specimens have exhibited the curved, transverse undulations on the chamber 
of habitation as shown in that species. The interiors of the specimens forming 
the basis of the present description, are filled with iron pyrites, and the shell 
has been dissolved and replaced by the same material. 
This fossil occurring in the Marcellus shale, which is regarded as a sub¬ 
ordinate member of the Hamilton group, is associated with an assemblage 
of species few of which extend beyond the horizon of this shale, and its 
included “ Goniatite limestone.” The principal fossils in this association are 
Euomphalus planodiscus, Orthoceras Marcellense, 0. fastis, 0. subulatum, Gomphoceras 
Fischeri, G. solidum, G. Conradi, Gyroceras transversum, Nautilus ( Discites ) Marcel- 
lensis, N. oriens, Goniatites Vanuxemi, G. discoideus, G. plebeiformis, Proetus Halde- 
mani, and several species and genera of Pteropoda and Brachiopoda. With 
the exception of Orthoceras subulatum, Gomphoceras Fischeri, and Goniatites dis¬ 
coideus, these species are restricted to this limited vertical range, and constitute 
a remarkable fauna, considering the position of the shales between the two 
prominent formations—the Upper Helderberg limestones and the Hamilton 
group proper. 
Formation and locality. In the carbonaceous shales of the Marcellus member 
of the Hamilton group, at Schoharie, N. Y. 
