460 
the whorl finally into contact is more gradual, so that the umbilical 
perforation is larger and the contact occurs in the usual way on the 
ventral side of the ananepionic substage, instead of on the dorsal 
side of the metanepionic substage, as in Trocholites. 
The whorl has short ventro-dorsal and longer transverse diameters, 
or broad whorls like many species of Trocholites, but is like a broad 
whorled typical nautilian form from the earliest stage and has not 
the kidney-shaped outline so common in sections, especially of the 
younger stages of the shell in Trocholites. 
The modifications of this outline through the flattening of the 
abdomen and lessening of the gibbosity of the sides occurs doubtless 
at different stages in different species, but in Schroederoceras angu- 
fatum and Saemanni it is fully developed only in adults. 
The contact furrow is well marked in the young and continues in 
some species to be a well-defined depression throughout life, becom- 
ing, however, somewhat less marked in the free part of the whorl or 
gerontic stage. In some species it is very faintly marked ap- 
parently before this stage is reached. It seems to be dependent 
upon the closeness of the coiling and involution, which is as a rule 
very slight at all stages in the ontogeny and all stages in the 
phylogeny. It is consequently somewhat remarkable that this zone 
should persist upon the dorsum of the shell so long after the whorl 
becomes free of pressure on that side in the gerontic stage. 
The siphuncle does not apparently, so far as is seen, materially 
change the position it has at the end of the first whorl. It may, as 
in Saemanni, become slightly more removed from the dorsum, but 
in angulatum it is very close to the dorsum, even in the ephebic 
stage. The walls of this organ are thick, and it is often preserved 
in the middle of loosely crystalline calcareous deposits under condi- 
tions which are not usually considered favorable for the preserva- 
tion of siphuncles. 
SCHROEDEROCERAS ANGULATUM. 
LITUITES ANGULATUM Saem. (Padentogr., iii, Pl. xxi, Fig. 1a-d, not 
c-@). 
Loc., Brevig, Norway. 
The original of the Zt. angudatus of Saemann (Fig. 1a—6) isin the 
Mus. of Comp. Zodlogy. It has a subquadragonal whorl in the 
ephebic stage with a flattened and slightly concave abdomen. The 
shape in cross section is peculiar and quite different from that in 
Fig. 1@. The abdomen on the living chamber is slightly elevated 
