868 



PAL2E0ST0L0QY OF NEW YORK. 



CYRTOCERAS — GYROCERAS. 



Considering the species in the order here followed, it is evident that one 

 genus must include the whole series. Besides the gradation exhibited in the 

 amount of curvature, there are conspicuous and almost constant features marking 

 nearly all the species, in the characters of the surface ornaments and the 

 position of the siphuncle. 



The nomenclature of the species remains essentially as originally published, 

 and will not be altered until a further revision of this subject can be made. 



List of the species of Cyrtoceras-Gyroceras described in this volume: 

 Cyrtoceras-Gyroceras. 



eugenium, Hall, Schoharie grit and Upper Hel- " 



derberg limestone 

 emulum, " Schoharie grit and Upper Hel- 



derberg limestone 

 " Upper Helderberg limestone. 



citum, " 



Nereus, " 



trivolve, Conrad, 



Matheri, " 



laciniosum, Hall, 



undulatum, Vanuxem, 

 paucinodum, Hall, 



Jason, " 



spinosum, Conrad, 

 transversum, Hall, 



validum, " 



Eryx, " 



Cyclops, " 



Slender forms, show- 

 ing a gradation 

 from curved to con- 

 volute 



Schoharie' grit 



(1 N 



Hamilton group . 

 Schoharie grit . 

 Hamilton group 

 Upper Helderberg limestone. 



Robust forms, show- 

 ing a gradation 

 from curved to con- 

 volute. 



