CEPHALOPODA. 367 



Cyrtoceras morsum. 



PLATE XLVII, FIGS. S. 4. 



Cyrtnceras morsum, Halt,. Descriptions of New Species of Fossils, etc., p. 43. 1861. 



Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 71, pi. 9, tig. 6. 1862. 

 " " " Illustrations of Devonian Fossils: Cephalopoda, pi. 46, figs 3, 4. 1876. 



Shell small, arcuate, making about one-fourth of one volution, exogastric. 

 The depth of the arc of curvature is six mm. in the length of thirty-six mm. 

 Transverse section circular. Tube regularly enlarging from the apex to the 

 aperture. Apical angle about 9°. 



The chamber of habitation has a length equal to the diameter of the tube 

 at the aperture. Aperture entire, slightly expanded, with a gentle sinus in 

 the margin on the ventral side. 



Air-chambers regular, numerous, increasing in depth from the apex to the 

 outer chamber, varying from one to three mm. in the length of thirty mm. 

 Septa not observed. Sutures straight and horizontal. 



Siphuncle near the convex ventral side; its other characters have not 

 been observed. 



Test thin, having a thickness of about .25 mm. Surface ornamented with 

 fine, lamellose, undulating lines of growth, and regular transverse ridges, 

 formed by an aggregation of the lines of growth. Sinus of the ornaments 

 on the ventral side small, but abrupt. 



A specimen, preserving the chamber of habitation with twenty-six attached 

 air-chambers, has a length of fifty-five mm., of which sixteen mm. pertain to 

 the chamber of habitation. Another specimen has been observed which 

 has nearly the same dimensions as the one given. 



This species is distinguished by its size, the transverse section, and the 

 apical angle. It differs from the apical portions of Gyroceras trivolve and 

 G. Matheri in its lesser curvature. From the apex of C. eugenium it is distin- 

 guished by its more cylindrical and less rapidly expanding tube, with the 

 sinus in the surface ornaments not so conspicuous. 



Formation and localities. In the Schoharie grit at Schoharie, and in the 

 Upper Helderberg limestone at Clarence Hollow, Erie county, N. Y. 



