208 
AUG. F. FOERSTE 
pressed, the siphuncle is exogastric, and the vertical outlines of 
its segments within the camerae are concave. 
It is evident that our knowledge of the cyrtoceroids of the Ca- 
nadian formations is very unsatisfactory. Of course, they would 
no longer be placed under the genus Cyrtoceras, as that genus is 
restricted at present. Cyrtoceras metellus Billings was referred 
by Hyatt^^ to his genus Maelonoceras, but the siphuncle segments 
of the latter are subfusiform, while those of Specimen No. 820a 
are strongly nummuloidal. 
10. ENDOCERAS HALL 
First described species: Endoceras subcentrale Hall, from the Black 
River (Watertown) at Watertown, New York. Pal. New York, 
vol. 1, 1847, p. 57. 
Accepted genotype: Endoceras proteiforme Hall. Pal. New York, 
vol. 1, 1847, p. 208 
Endoceras belongs to the group of genera in which the septal 
necks extend posteriorly until in contact with the septum next 
beneath. It is distinguished from other genera by the presence 
of long endocones which taper downward gradually to a point. 
The sides of these endocones are not in contact with the walls of 
the siphuncle but are free along their entire length. In typical 
Endoceras the endocones are few and distant from each other. 
Those species in which the endocones are numerous have been 
placed by Hyatt in his genus Vaginoceras. 
In distinguishing Vaginoceras from Endoceras, Hyatt stated^® 
that in Endoceras the septal necks extend posteriorly from one 
septum only as far as the septum next beneath, while in Vagino- 
ceras the septal necks extend beyond the next lower septum. It 
would require a monographic study to determine to what extent 
either the presence of numerous endocones or the long backward 
extention of the septal necks might be regarded as of generic 
value. It is still more doubtful if it is possible to distinguish a 
genus (Vaginoceras) in which the septal necks are more than one 
camera in length, and in which the endocones are numerous, from 
another genus (Endoceras) in which the septal necks are only one 
camera in length and in which the endocones are relatively few. 
Apparently, if Vaginoceras is to stand, its validity must be based 
upon one of these criteria alone, and not on both. The one here 
selected is the presence of numerous endocones, since Endoceras 
midtitahulatum Hall is the genotype of Vaginoceras. 
14 
Hyatt, A., op. cit., p. 280. 
Idem, p. 266. 
13 
