557 
great rapidity upon the venter in order to swing that part around 
the very sharp curve made by the gyroceran bend. 
The paranepionic substage has well-marked longitudinal ridges 
and transverse bands of growth given in Fig. 6. The latter part 
of the paranepionic in this species, if this be properly limited by 
means of the ornamentation, is close coiled. ‘That is to say, it 
touches dorsum of the ananepionic and envelops it, the involution 
being almost complete from the very beginning. 
The umbilical perforation is, however, not completely closed nor 
is it subsequently closed by extra growths of shell as in Maw¢c/us 
pompilius. The area of the umbilical zones is marked off at an 
early age by the smoothness of the shell, the longitudinal ridges 
being absent on these parts. In some specimens the shell mark- 
ings are much stronger than in others, but in all they seem to grow 
more decided until near the end of the metaneanic substage. 
The meta- and paranepionic substages have an elevated subangu- 
lar abdomen not shown in any of the figures, the outliné of the 
section of the whorl is in reality in these early substages depressed 
subtrigonal similar to the young whorl of Cymatoceras, but less 
acute, and to that of Mautelis pompitius, but more pronounced than 
in that species on account of the subangularity of the venter; the 
venter of Mautilus pompilius being more rounded in the paranepi- 
onic substage. 
The ananeanic and metaneanic are blended and probably not 
separable, but the paraneanic can be distinguished. The former 
has the siphuncle tending more towards the centre, although in 
some specimens this alteration is not so great as in others. ‘The 
transverse bands become broader and their edges have tubercular- 
like short ridges on a secondary band, which are sometimes well 
marked off on their apical borders from the sunken younger parts 
of the same bands of growth. ‘These ridges are always continuous 
from band to band and over the sunken parts of each band. In 
the paraneanic substage, as shown in Figs. 7 and 8, these ornaments 
begin to diminish and finally die out. In Fig. 8 this substage is 
limited by the retention on one side of a partial constriction or 
permanent aperture, which, however, is not present in all shells. 
In the anephebic stage, also shown in Figs. 7 and 8, orad of the 
constriction, the shell is very nearly as smooth as it is in the full 
grown. The form of the whorl remains about the same. The 
siphuncle has become dorso-ceatren in position in this shell, in 
