CEPHALOPODA. 317 



tral diameters of G.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, Mcnster, 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. fustis, 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. 



