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PALEONTOLOGY OF NEW YORE. 
GYROCERAS, De Koninck. 1841. 
This genus has been variously constituted and defined by different authors to 
include forms showing a greater curvature of the tube than in typical forms 
of Cyrtoceras, and without the contiguity of the volutions, as in the genus 
Nautilus. With these characters as a basis, it has been made the receptacle 
of numerous unlike species, agreeing only in the amount of curvature. The 
original types of the genus have little resemblance to the species described by 
other authors, and have since been removed to form the type of another 
distinct genus. The very thorough and complete digest of the allied genera 
by M. Barrande does not appear to have furnished such information as can 
be satisfactorily applied to the determination of the relations of the species here 
described. 
HISTORICAL SKETCH. 
The first recognition in America of the genus Gyroceras, as defined and 
established by De Koninck, was in 1844, by Dr. D. D. Owen, in his Report of a 
Geological Exploration of Parts of Iowa, Wisconsin and Illinois;* where he described 
the species Gyroceras cornutum, from the Devonian system of Iowa. 
In 1840 Mr. T. A. Conrad described Phragmoceras spinosum [=G. spinosum \, 
Cyrtoceras Matheri and Cyrtoceras trivolve [= Gyroceras] , from the Upper Held- 
erberg group (Ann. Rep. Geolog. Surv. of N. Y.: Pal. Dept.). 
In 1843 Mr. L. Vanuxem described Cyrtoceras undulatum , from the Upper Hel~ 
derberg group (Geolog. Surv. of N. Y.: Rep. Fourth Dist.). 
In 1852 Dr. Owen described G. Burlingtonense \—Nautilus] , from the Lower 
Carboniferous system (Geolog. Rep. of Wisconsin, Iowa and Minn.). 
In 1853 Dr. Saeman described G. expansum [—Nautilus bucinurn] (Dunker and 
von Meyer: Palceontographica, vol. 1). 
In 1857 Mr. E. Billings described G. Americanus, from the Upper Silurian 
system; G. magnificum [—Lituites magnificum ], from the Iludson-river group; and 
G. vagans, from the Black-river group (Geolog. Surv. of Canada: Rep. of Progr.). 
* Bearing- the date of 1840, althoug-h revised and iirst published in 1844. 
