514 
mic sinus, lateral crests and dorsal crests bending inwards and con- 
tracting the opening. It is also of interest in this connection as 
showing how narrow and comma-shaped the umbilical perforation 
may be without affecting the form of the dorsum, and especially 
with regard to the history of the degeneration of the impressed 
zone on the dorsum of the free whorl and living chamber. 
Ophidioceras. 
OPHIDIOCERAS RUDENS. 
OPHIDIOCERAS BARRANDE (Sys¢. Sz/., Pl. xlv); Pl. vili, Figs. 29-35. 
Loc. Bohemia. 
This species has a flattened comma-shaped umbilical perforation 
and, although the increase in size is rapid, it is not excessive in 
the lateral diameters as compared with the ventro-dorsal from the 
ananepionic substage to the paranepionic. ‘The result is a volution 
which curves evenly about the core of the perforation and preserves 
the rounded dorsum and the general aspect of the section without 
great modification throughout the nepionic stage. The cicatrix is 
well-marked, as shown in Fig. 30, and the ananepionic substage 
has an elongated ventro-dorsal and short transverse diameter. 
In the metanepionic substage the whorl becomes broader on the 
venter than on the dorsum, and in the paranepionic the dorsum 
spreads, becoming broader, but does not quite equal the venter in 
breadth. In the ananeanic substage the longitudinal ridges become 
more prominent and more easily observable and the costations also 
appear. 
The contact furrow begins as soon as contact is complete and is 
at once deep and definitely defined, as a hollow fitting over the 
ananepionic tip, and it completely covers in this substage. The 
contact takes place on the dorsal side of the ananepionic substage 
and the furrow is deeper at this point in proportion to the whorls 
than it is at any subsequent age. 
There were two specimens showing the nepionic stages of this 
species under observation, the one drawn and this one. Both 
exhibit the peculiar globular form of the apex, and the well-defined 
ana- and metanepionic substages, which can be quite closely com- 
pared with those of autilus pompilius, and they have similar con- 
strictions to the first two constrictions depicted in Henry Brook’s 
drawings on Pl. i of this paper. 
