515 
The dorsum of the whorl becomes at the same time broader and 
the whorl alters in shape to an approximately kidney-shaped outline 
with the ventro-dorsal, shorter than the transverse diameter. After 
this age the increase of growth proceeds more slowly. Inthe meta- 
neanic substage, the costz and longitudinal ridges become well 
developed, but the venter remains rounded and the lines of growth 
show a deep, broad hyponomic sinus and lateral crests, and the 
aperture at this stage must have been very distinct from that of the 
next substage. 
In the paraneanic substage the central ventral zone appears at first 
as a broad band, in low relief, arising obviously from the elevated 
edges of the narrow hyponomic sinus, which begins to appear at 
this age. In the anephebic stage, at the beginning of the third 
volution, this acquires its specific prominence and characters. The 
metephebic stage is introduced by the subsequent moulding of the 
dorsum over this broad carination which modifies the outline of the 
contact furrow in section, and gives it the peculiar central dorsal 
face and narrow lateral dorsal faces as peculiar to this genus as are 
the ventral modifications which give rise to them.* 
The sutures do not seem to be much modified after the nepionic 
stage is passed by. ‘The czcum, if a spot observed on the broken 
apex of one specimen is correctly translated, is subventran or nearly 
so in the first or metanepionic septum and the siphuncle is about 
the same position relatively or propioventran in the paranepionic 
substage as observed in two specimens and given in one of these, 
Fig. 30, Pl. viii, and then changes slowly to centroventran in the 
anephebic substage. The living chamber is very long, being, if the 
excentric free part were applied to the coil, almost one volution in 
length. It is, as has been described by Barrande, present in small 
(young?) shells, but I doubt its existence, as well as that of the pecu- 
liar ophidioceran aperture, before the substage in which the ventral 
zone appears. 
The free whorl in this genus is specially interesting, because even 
in large shells the impressed zone is preserved on the dorsum in a 
very significant way. It is well known that most of the shells, if 
not all of this genus, have the lituitean bend, that is to say, the free 
living chamber, after it becomes free and excentric, bends suddenly 
ventrally, as in Fig. 27, Pl. viii, making the last part of the living 
* This is usually called a keel or carina, but it is a modification of a different kind and 
sometimes has keels upon its borders. 
