537 
the figure, is approximately given. This form is like that of the 
arcuate forms of genus Tripteroceras in their ephebic stage. The 
shell was smooth. A paranepionic septum is shown below and in 
the specimen (Figs. 36-37) a still younger septum was developed 
after this drawing was made. ‘These have ventral saddles, very 
faint lateral lobes, and minute shallow dorsal lobes, resembling in 
shape those of the older stages. 
As shown in these drawings, the dorsum of the nepionic stage, 
which ends with the section just below the apex, is rounded and 
the impressed zone is a contact furrow beginning in the ananeanic 
substage only after the whorls touch. This zone deepens rapidly, 
but is never very broad or deep. 
The side view shows the cyrtoceran form of the metanepionic 
substage and the large size of the umbilical perforation, which is 
given by a dotted line. 
The siphuncle is nearly subventran in the paranepionic substage, 
but it does not increase proportionately in size and becomes cen- 
troventran in the neanic septum as shown above the apex, and 
ventrocentren in the ephebic stage. 
The lateral angles are more acute and the form more perfectly 
digonal in the neanic and early ephebic stage than in the paranepi- 
onic or gerontic stages. 
The specimen figured is in Museum of Comparative Zodlogy. 
A young specimen of this species from Windsor, N. S., in the 
Museum at Ottawa, shows the living chamber of the early ephebic 
stage or paraneanic substage at the end of the second whorl. ‘This 
is not quite one-half of a volution in length and has a deep, rather 
narrow hyponomic sinus with large median lateral crests and deep 
sinuses near the lines of involution. 
Lophoceras. 
This genus, described in Fourth Annual Report Geological Sur- 
vey of Texas, has a very slight impressed zone in some species and 
it is clearly dependent upon the contact of the whorls. 
Potoceras.* 
POTOCERAS DUBIUM, n. sp. Pl. x, Figs. 15-22. 
Loc. (?). 
The nepionic stage is shown enlarged in Figs. 16-18, Pl. x, and 
* [léto0s, drinking. 
PROC. AMER. PHILOS. SOC. XXXII. 143.3 P. PRINTED JULY 13, 1894. 
