CEPHALOPoi-A 7'.I7 



Family ONCCKT.KATIh I 



Dm CUNnCKUAS. Ma-ckr. 



I'M'. UrMI.tiKOKMK H "/!///> //, 



I'l \ IK I. VII HiiS 7-10. 



O*eoera* mumitiformr Win IHKLI>. !>. Ann. I; Surv, Wisconsin, p. 68. 



Oneoernu m*mia/ormr \\ in 1 1 IKI.D, 1882. Oeolutfjr of Wlnconsln, vol. Iv., p. 232, pi. vn, ttg. 



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 

 -ut ures are slightly undulating and are stated to form a minute dorsal lobe although 

 tin- -ipho 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 

 piv-.T\r-i -pfcimrn- of tin- IpMiM occur 111 t lie Miniif-ota collection-, ami after 



an examination of the original material, I refer to the species an unusually tine 

 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 i- 

 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 ram. 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 

 1- mm. The shell is not equiconvex; the swelling just below the constriction is 

 much more consi.li-r.ihle 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 uuexposed, their siphonal punctures may prove to 

 more nearly agree in position with those of the type-species of the gt-nu-. In some 

 of the internal casts the position of the sipho is somewhat excentric and is dis- 



ZlMclir.dr4Mtnh.|olo.OaMUMh. oJ. iiTllL p.*. pi. u If*. 



