CEPHALOPODA. 359 



In 1860 J. Hall described G. gracile, from the Goniatite limestone of Indi- 

 ana ; G. liratum [=Nautilus liratum] and Cyrtoceras transversum, from the Gonia- 

 tite limestone of the Marcellus shale (Thirteenth Rep. N. Y. State Cab. Nat. Hist.). 



In 1861 J. Hall described G. Cyclops, G. Eryx, G. Nereus, Cyrtoceras eugenium 

 and C. Jason, from the Upper Helderberg group ; and Gyroceras Nais [=Por- 

 cellia Nais], from the Chemung group (Descriptions of New Species of Fossils). 

 The same species were republished in the Fifteenth Rep. N. Y. State Cab. Nat. 

 Hist, in 1862. 



In 1862 Mr. Richard Owen described G. rhombolineare [= Trochoceras] , from 

 the Silurian system of Indiana (Geological Reconnoisance of Indiana, page 36). 



In 1865 Messrs. Winchell and Marcy described G. Bannisteri [=Trochoceras 

 Bannisteri], from the Niagara group (Mem. Bost. Soc. Nat. Hist.). 



In 1806 Messrs. Meek and Worthen described Nautilus (Cryptoceras) Rockfor- 

 densis, from the Kinderhook group (Proc. Acad. Nat. Sci. Phila.). In 1868 the 

 authors referred this species to the genus Gyroceras? (Geolog. Surv. Illinois,vo\. 3). 



In 1868 Mr. J. W. Dawson described G. Hartti, from the Carboniferous sys- 

 tem (Acadian Geology). 



Mr. F. B. Meek described G. Logani, from the Devonian system (Trans. 

 Chicago Acad. Sci.). 



Meek and Worthen described G? constrictum, from the Hamilton group (Geolog. 

 Survey of Illinois, vol. 3). 



In 1871 Mr. Meek described G. inelegans [== Nautilus] and G. Ohioensis [== Nau- 

 tilus], from the Upper Helderberg group (Proc. Acad. Nat. Sci. Phila.). 



In 1876 J. Hall described G. paucinodum and G. validum, from the Upper 

 Helderberg group, and G. subliratum [=Nautilus subliratum], from the Hamilton 

 group (Illustrations of Devonian Fossils). 



In 1879 J. Hall described G abruptum, from the Niagara group of Indiana 

 (Trans. Alb. Inst., vol. 10). 



The historical notices and remarks on these genera are introduced here to 

 facilitate a comparison, and to avoid separating species which must unavoid- 

 ably appear in the consideration of either genus. The well-defined species 



