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 Orlhoceras Trentonensis [= Cyr¬ 
toceras Trentonense], from the Trenton limestone ( Geolog. Surv. of N.fY.: 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 undulatum ], 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. suhannulatum, d’Orb., 1850], C. macrostomum and C. multicameratum, from 
the Black-river and Trenton groups; and C. arcuatum (not C. arcuatum, Steinin- 
ger, 1830) \=C. subarcuatum, d’Orb., 1850], C. camurum, C. constridostriatum and 
C. lamellosum (not C. lamellosum, d’Arch. and de Yern , 1842) \=C. Hallanum, 
d’Orb., 1850], from the Trenton group (Palaeontology of New York, vol. 1). 
In 1852 J. Hall described C. ardicameratum, from the Guelph group, and 
C. cancellatum (not C. canccllatum, Rcemer, 1844) [=C. subcancellatum, Hall, 1877], 
from the Niagara group (Palaeontology 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. subturbinatum, 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). 
