495 
depressed oval, as shown in Barrande’s figures. Fig. 17 gives a 
cut farther in towards the narrower part of the umbilical perforation 
and shows the paranepionic substage younger than in Fig. 16, and 
with more depressed and approximately digonal outline. Above 
this the paranepionic whorl is older than in Fig. 16, and with a 
more decided impressed zone and broader transverse diameter ap- 
proximating to the nephritic shape. 
In Fig. 18 the cut has passed beyond the perforation and shows 
the paranepionic volution above when it first touches the dorsum of 
the metanepionic or ananepionic substage below. ‘The latter is 
distorted because the cut goes through the inner or dorsal side of the 
curve of the metanepionic and ananepionic substages. The oval in 
the centre is apparently due to a cut through the fundus of the first 
‘ septum, which must be deeply concave. In Fig. 19 the cut has 
approached nearer the ventral side of the apical chamber and is 
apparently wholly within this and shows the increase in depth of 
the impressed zone as the ananeanic substage begins and also the 
decidedly nephritic outline which this at once assumes. ‘This also 
shows that the digonal outline of the volution below the centre 
belongs to the neanic stage. In Fig. 20 the cut has passed close to 
the outer side of the ananepionic substage and as in the centre it does 
not intersect any septum it is probably wholly within the apical 
chamber. This chamber must be very deep, as it is in Hercoceras 
and some other forms. The broader shaded outline of the ananep- 
ionic substage is the shell which is cut obliquely by the section. 
The sections of the ananeanic whorl above and the metaneanic 
below intersect a number of septa and show the passage to the 
farther side of the umbilical perforation from that with which the 
series began in Fig. 16. 
Temnocheilus. 
This genus is very similar in its general aspect to Hercoceras and 
Anomaloceras, but it has distinct young and this shows that it has 
been directly evolved from a cyrtoceran form and not from either of 
these nautilian genera. 
The form known as Gyroceras proximum, sp. Barrande, Pl. ciii, 
has the tuberculations on the lateral angles, a trapezoidal whorl, 
the siphuncle subventran and sutures and impressed zone as in this 
genus, but until it is better known it is not practicable to decide 
whether it belongs to this genus or to Hercoceras. 
