CEPHALOPODA. 355 



HISTORICAL SKETCH. 



The genus Cyrtoceras was first recognized in America by Mr. T. A. Conrad, 

 who, in 1838, described Cyrtoceras maximus [= Nautilus maximus\, from the 

 Hamilton group (Geolog. Surv. of N. Y. : Pal. Dept., Annual Report). 



In 1840 [1844] Dr. D. D. Owen described C. conicum, from the upper Magne- 

 sian limestone = Galena limestone (Report on the Geological Explorations of Parts 

 of Iowa, Wisconsin, and Illinois). 



Mr. Conrad described C. trivolvis [=Gyroceras trivolve] and C. Matheri 

 \==Gyroceras Matheri], from the Upper Helderberg group (Geolog. Surv. of N. Y.: 

 Pal. Dept., Annual Report). 



In 1842 Mr. E. Emmons published C.filosum and Orthoceras Trentonensis [= Cyr- 

 toceras Trentonense], from the Trenton limestone (Geolog. Surv. of N Y.: Rep. 

 Second Dist.). 



In 1843 Mr. Conrad described C. marginale (not C. marginale, Phillips), (Proc. 

 Acad. Nat. Sci. Phila., vol. 1). 



Mr. Lardner Vanuxem described C. undulatum [=Gyroceras undulaturn\ , -from 

 the Upper Helderberg limestone (Geolog. Surv. of N. Y.: Rep. Third Dist.). 



In 1847 James Hall described C. annulatum (not C. annulatum, Goldfuss, 1832) 

 [=C. subannulatum, d'Orb., 1850], C. macrostomum and C. multicameratum, from 

 the Black-river and Trenton groups; and C. arcuatum (not C. arcuatum, Steinin- 

 oer, 1830) [=C. subarcuatum, d'Orb., 1850], C. camurum, C. constrictostriatum and 

 C. himellosum (not C. lamelhsum, d'Arch. and de Vern , 1842) [=C. Hallanum, 

 d'Orb., 1850], from the Trenton group (Paleontology of New York, vol. 1). 



In 1852 J. Hall described C. arcticameratum, from the Guelph group, and 

 C. canc.ellalum (not C. cancellatum, Rcemer, 1844) [==C. subcancellatum, Hall, 1877], 

 from the Niagara group (Paleontology of New York, vol. 2). 



In 1857 Mr. E. Billings described C. falx, C. regulare and C. simplex, from 

 the Black-river and Trenton groups; C. sinuatum, from the Black-river group; 

 and C. suhturbinalum, from the Chazy and Black-river groups (Geolog. Survey 

 of Canada : Report of Progress). 



In 1858 Prof. G. C. Swallow described C. dorsatum, from the Permian system 

 (Trans. St. Louis Acad. Sci., vol. 1). 



