356 TWENTIETH REPORT ON THE STATE CABINET. 



ORTHOCERAS NIAGARENSE (n.s.). 



PLATE 20-(ll), FIG. 3. 



Shell elongate, gradually tapering; section broadly elliptical; septa 

 deeply concave, depth of chamber about five lines where the diameter 

 is one and a half inches ; siphuncle excentric. Surface annulated by low 

 rounded undulations which are from one to two lines distant, according 

 to the size of the shell ; intermediate spaces regularly concave. In the 

 larger parts of the shell there are about three annulations to each cham- 

 ber. The finer surface markings unknown. 



This species in its young state is rather slender and very gently taper- 

 ing, and, though attaining a pretty large size, is not as robust as most of 

 the associated forms. It bears considerable resemblance to the Niagara 

 shale species which I have referred with doubt to the O. imhricatum, 

 Wahl.; but the annulations are not so sharply elevated, and the septa are 

 comparatively more distant. The section, in all the specimens examined, is 

 elliptical. It is possible that this may be the species described by Mr. 

 Billings under the name O. oberon^ the principal difference being in our 

 specimens the prevailing elliptical form of the tube. 



The specimen figured is about nine inches in length, and is represented 

 of the natural size. 



Formation and locality. In limestone of the age of the Niagara group, 

 at Waukesha and Pewaukee, Wisconsin, 



GENUS CYRTOCERAS^^ (GoLDFuss). 



CYRTOCERAS BREVICORNE (n.s.). 



PLATE i5.«(-e^, FIGS. 8 & 9. 



Shell small, gently curving and very rapidly expanding from the apex, 

 the diameter of the outer chamber nearly equalling one half of the 

 entire length of the shell ; septa somewhat closely arranged, curving 

 upward on the dorsum, moderately concave, the four c>uter ones measur- 

 ing five-eighths of an inch on the back and less than half an inch on the 

 ventral side. Siphuncle small, and lying close to the dorsal margin. 

 Surface of shell unknown. 



This species is the most rapidly expanding form of any yet discovered 

 in these rocks, and may be easily distinguished by this feature alone. The 

 specimen figured retains a single chamber besides the outer one, the 

 remaining portions being restored from the impression in the adhering stone. 

 Another fragment retains the chamber of habitation, and six of the septa 

 below. The fossil is associated with a smaller species of Cyrtoceras {C. 



* See page 45 of the original paper, page 349 of this Report, where species of this genus 

 are described. The delay in the final printing of the Report has given opportunity for 

 further investigation among the collections and other species of this, and other genera 

 have been determined. 



