CEPHALOPODA. 3G9 



Cyrtoceras eugenium. 



PLATES XXXVI, FIG. 5; XL VII, FIGS. 5-7; XCVI, FIGS. 1-11 ; XCVII, FIGS. 10, 11. 



Cyrtoceras eugenium. Hall. Descriptions of New Species of Fossils, etc., p. 42. 1861. 



Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 70, pi. 9, figs. 1-3. 1862. 

 " " " Illustrations of Devonian Fossils : Cephalopoda, pi. 46, fig's. 5-7. 1876. 



Orfkoeera* foliatm/i. " Descriptions of New Species of Fossils, etc., p. 42. 1861. 



Fifteenth Rep. N. Y. 8tate Cab. Nat. Hist., p. 70, pi. 9, figs. 1-3. 1862. 



Shell slender, apical portion curved, making about one-fourth of one volution. 

 Tube nearly straight for a length, measured from the aperture toward 

 the apex, equal to one-half the entire length of the shell. In the larger 

 individuals the length of the straight portion is comparatively greater. 

 Transverse section subcircular, somewhat flattened on the dorsal and ventral 

 sides along the straight portion of the tube. Tube regularly enlarging 

 from the apex to the aperture, becoming slightly gibbous over the anterior 

 half, and contracting very gradually toward the aperture, where it is some- 

 what expanded. Apical angle about 10°. 



Chamber of habitation with a length one-half greater than the ventro- 

 dorsal diameter of the tube at the last septum; slightly contracting toward 

 the aperture, where it more rapidly expands. Crenulations marking the 

 cust of the tube throughout its length, showing as irregular, indistinct, 

 rounded furrows and ridges. Aperture entire, with a deep rounded sinus in 

 the ventral margin, corresponding to the sinus in the ornaments of the 

 test. 



Air-chambers regular, having a depth of six mm. near the grand chamber. 

 Toward the apex they are shallower, and show a considerable variation in 

 depth ; one specimen presents a variation of from four to six mm. in the 

 length of twenty mm. Septa smooth, thin, having a concavity greater 

 than the depth of the air-chambers, apparently independent of the surface 

 characters. Sutures straight and horizontal, but slightly impressed on the 

 internal mould. 



Siphuncle small, submarginal, exposed in the process of weathering, hav- 

 ing a diameter of three mm. where the tube measures thirty mm. 

 47 



