473 
shown in Whitfield’s figure, Pl. xxxii, and in my figure, the oldest 
sutures are more sinuous than those of an earlier stage just under 
the free part of the living chamber, as given in my copy of his 
figure, with sutures drawn in from the original chambers (Fig. 28, 
Pl. vi). They have normally in the ephebic stage ventral and 
dorsal lobes, with lateral lobes and saddles at the abdominal angles 
and umbilical shoulders. : 
The length of the living chamber in a full-grown specimen is 
over one-half a volution, and the latter part is free, as given by 
Whitfield and in my Fig. 7, Pl. vii. 
SCHROEDEROCERAS CASINENSIS. 
LiruirEs EaToni, var. CASINENSIS. Whitf. (Buldet. Am. Mus., 
New York, i, No. 8, Pl. xxxii). Pl. vi, Figs. 36-38, and PI. 
vii, Figs. 4-6. 
Loc., Fort Cassin, Lake Champlain. 
This is a distinct species, the sutures being straighter in the 
ephebic stage than in true a/¢oni, the venter and sides are more 
decidedly flattened, and the relative proportions of the last whorl 
at the same age different.* The ventro-dorsal and transverse 
diameters are about equal, whereas in Ha¢oni the transverse is con- 
siderably longer than the ventro-dorsal in the mesal plane. The 
amount of involution in Hafonz and the depth of the contact furrow 
in the ephebic stage is also greater. | 
Whitfield’s figure is given on PI. vi, Fig. 36, with some emen- 
dations taken from the original specimen. ‘This shows that the 
ephebic stage had not a free living chamber, and that shown in my 
Fig. 4, Pl. vii, represents the gerontic stage. The front view, 
Fig. 5, shows the deeper contact furrow and the dorsal lobes in 
the dorsum of the metephebic substage and the slight but imper- 
ceptible change which takes place in the broader, shallower zone of 
the early part of the gerontic living chamber below. ‘The free 
part of this chamber is at first concave just beyond the broken end 
of the metephebic whorl, then flattened, and finally convex on the 
dorsum, as shown in Figs. 5 and 6. 
The length of this living chamber was nearly three-fourths of a 
volution, beginning somewhat beyond the broken part given in 
* Whitfield himself thought this was probably a distinct species, as shown by his 
remarks on page 332. 
PROC. AMER, PHILOS. SOC. XXXII. 148. 8H. PRINTED JUNE 28, 1894. 
