CEPHALOPODA. 797 
Clinoceras mumiaforme.] 
Family ONCOCERATID 4. 
Genus CLINOCERAS, Mascke, 1876. 
CLINOCERAS MUMI@FORME Whitfield, 1878, 
PLATE LVII, FIGS. 7—10. 
Oncoceras mumiaforme WHITFIELD, 1878. Ann. Rept. Geol. Surv, Wisconsin, p. 58. 
Oncoceras mumiaforme WHITFIELD, 1882. Geology of Wisconsin, vol. iv., p. 282, pl. vil, figs. 3—-5. 
Mascke founded this genus* upon a shell, C. dens, from the Silurian boulders of 
North Prussia, characterized by its gently arcuate form, the slender proportions of 
its early parts, the expansion of the body-chamber, and broad, rather deep constric- 
tion near the aperture. The aperture itself is regular and not contracted. The 
sutures are slightly undulating and are stated to form a minute dorsal lobe although 
the sipho is not marginal but lies between the center and the ventral side in the 
adult chambers. 
The species which is herewith referred to this genus was described from rather 
imperfect material, virtually internal casts of but parts of the shell. Similarly 
preserved specimens of the species occur in the Minnesota collections, and after 
an examination of the original material, I refer to the species an unusually fine 
example which, in form and proportions, is almost a replica of Mascke’s type. This 
shell, as preserved, is nearly complete, the aperture and external surface being 
retained and nothing wanting but a small portion at the apex. Its length is 
66 mm.; its original length was probably about 70 mm. Its aperture which is 
essentially circular has a diameter of 10 mm., and at a distance of 8 mm. below the 
aperture the broad constriction is deepest. From the aperture to the greatest 
elevation of the swelling below it is 16 mm. and at this point the diameter of the 
shell is 10 mm. The distal extremity of the shell measures 3.5 mm. in diameter. 
The cross-section of the shell is circular at every point. The arcuation of the shell 
or divergence from the vertical let fall from the center of either extremity is 
12 mm. The shell is not equiconvex; the swelling just below the constriction is 
much more considerable on the outer or convex curve of the shell, and this differ- 
ence is perceptible though not so distinct over other portions of the body-chamber. 
‘No septa are exposed except the terminal one, and that is evenly convex in all 
directions and bears a central sipho. This, however, is a very early septum, and 
though the maturer septa are unexposed, their siphonal punctures may prove to 
more nearly agree in position with those of the type-species of the genus. In some 
of the internal casts the position of the sipho is somewhat excentric and is dis- 
* Zeitschr. der deutsch. geolog. Gesellsch. vol. xxviii, p. 49, pl. 1. 1876. 
