67 
A study of the types of Cameroceras trentonense in connexion with 
specimens occurring in the United States National Museum suggests that 
the chief difference between Endoceras and Cameroceras consists in the 
character of the endocones. In Endoceras these are strictly cones, from 
their origin at the walls of the siphuncle to their pointed ends which 
terminate near the centre of the cross-section of the siphuncle at some 
more or less remote point beneath. In Cameroceras, on the contrary, 
that part of the structure which is comparable with the endocones of 
Endoceras is conical only at the base. Here, for a length corresponding to 
that of three to six segments of the siphuncle, the endocone is conical 
in form, but excentric in position, the pointed end terminating near or in 
contact with the ventral wall of the siphuncle. Above the conical portion 
of the endocone its walls appear to conform for a length of four or more 
earner® with the shape of the siphuncle, this part having the form of a 
cylindrical body more or less conspicuously annulated in a diagonal direc- 
tion. The conical part at the base is filled with a calcareous deposit, 
its upper part thinning, until, a short distance above the top of the conical 
portion, this deposit has thinned to the average thickness of the walls of 
the siphuncle. The structure is that of Nanno. 
The genus Endoceras was described by Hall, 1 and no type was 
designated. The species described first under this generic designation 
is Endoceras subcentrale Hall. Plate XVII, figure 4, accompanying the 
original description of this species, is printed upside down, and only the 
middle half of the type specimen is included. The type specimen exposes 
an endocone, as in the figure; the septal necks have a length of two earner®, 
invaginating into the funnels next beneath. 
In Bassler’s “Bibliographic Index of American Ordovician and 
Silurian Fossils, 1915”, Endoceras proteiforme Hall is stated to be the 
accepted type. In Zittel-Eastman’s “ Text-book of Palaeontology,” 
Endoceras proteiforme is figured, and under Endoceras it is stated that 
“Funnels reach from septum of origination to the next apicad, but no 
farther.” 
Hall, at the time of his original description of the genus Endoceras, 
had no clear conception of the variation in the distance to which the 
septal necks extended downward in different species of Endoceras. His 
attention was centred on the endocones, which he regarded as the 
characteristic feature of Endoceras. Therefore, he did not differentiate 
between forms whose septal necks extended downward only as far as the 
septum next beneath and those whose septal necks extended considerably 
farther. Nor did he differentiate between forms having numerous endo- 
cones and forms having only few. The writer has not seen any specimens 
with numerous endocones, such as those figured by Hyatt in Zittel- 
Eastman. 
Endoceras proteiforme is figured by Hall on Plates 48, 49, 50, and 53, 
accompanying the original description. On Plate 48, figure 4 is described 
first, and this is regarded as the type of the species. In this type six 
earner® occur in a length equal to the diameter of the conch, at the top 
of the series being counted. 
1 Pal . of New York, vol. I, p. 58 (1847). 
