368 
PALAEONTOLOGY 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 
cemalum, 
cc 
Schoharie grit and Upper Hel- 
derberg limestone 
citum, 
cc 
Upper Helderberg limestone. 
Nereus, 
cc 
CC CC 
involve, 
Conrad, 
cc cc 
Matheri, 
cc 
cc cc 
laciniosum, 
Hall, 
cc cc 
undulatum, 
Vanuxem, 
cc cc 
pancinodum, Hall, 
cc cc 
Jason, 
CC 
Schoharie grit 
spinosum, 
Conrad, 
CC cc 
transversum, Hall, 
Hamilton group 
validum, 
CC 
Schoharie grit . 
Eryx, 
CC 
Hamilton group 
Cyclops, 
cc 
Upper Helderberg limestone. 
Slender forms, show¬ 
ing a gradation 
from curved to con¬ 
volute, 
Robust forms, show¬ 
ing a gradation 
from curved to con¬ 
volute. 
