358 PALMOSTOLOQY OF SEW YORK. 



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. spi?wsum\, 

 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 bucinum] (Dunker and 

 von Meyer: Palaontographica, vol. 1). 



In 1857 Mr. E. Billings described G. Americanus, from the Upper Silurian 

 Bystem; G. magnificum [=Lituites magnificum], from the Hudson-river group; and 

 G. vagans, from the Black-river group (Geolog. Surv. of Canada : Rep. of Progr.). 



•Bearing the date of 1810, although revised and first published in 1844. 



