483 
existence of lateral depressions or open nepionic umbilici, and the 
usual umbilical perforation is present, although rendered very small 
by the closeness of the coiling. 
The first air chamber observed in two specimens is unusually 
deep and broadens laterally by growth with extreme rapidity. I 
have not been able to expose a complete apex so as to see the cica- 
trix, but have seen the outline of the umbilical perforation at the 
centre. The siphuncle is closed at the end, but not perceptibly 
swollen into a pouch as in most Nautiloids. It is not close to the 
dorsum in the first chamber, but the cecal end is centren as shown 
in the section of the ananepionic substage (Fig. 24, Pl. iv). 
It clings closely to the dorsal side as in the young of ¢¢ernastriata, 
as shown in Fig. 25, which represents a truncated apical chamber and 
the paranepionic substage of the first whorl. Holm and Schréder’s 
observations have shown that it is ellipochoanoidal or has in other 
words short funnels and a porous wall between contiguous septa. 
Schréder’s observations apply to the full-grown shell and Holm’s to 
the young.* 
The extremely rapid expansion of the whorls ceases before the 
first whorl is completed, but it gives to the nepionic shell, when seen 
from the venter, the aspect so common in Ammonoids during what 
is usually called the goniatic stage. So far as now known to me, 
no other Nautiloid possesses this peculiarity to such a remarkable 
degree in the nepionic stage, Fig. 39, Pl. vi. 
The mode of growth of the siphuncle is independent of the close 
coiling, since it has the same history in Zrocholites tnternastriata, 
with a large umbilical perforation, as in true Trocholites of later 
times, with a more minute perforation. 
The septa as in most nautiloids are much wider apart, at first 
gradually decreasing until the end of the first whorl or thereabouts, 
as shown in Holm’s figures, when they assume the normal distance 
and are less deeply convex. The sutures exhibit corresponding 
differences, having large ventral saddles, deep lateral lobes and 
probably, although these were not clearly seen, dorsal saddles in 
these earlier stages. 
The lines of growth are much straighter in the nepionic stage 
than subsequently. - The hyponomic sinus is so broad and shallow 
that it is hardly observable on the third quarter of the first whorl 
* Holm’s observations and mine are similar and I have reproduced his figure in Pl. iv 
of this paper. 
