541 
Vestinautilus Konincki leads into such forms as Vestinautilus pin- 
guts, Figs. 16-19, which has the ridged characters, etc., confined 
to the nepionic stage, which is somewhat abbreviated. The sub- 
spinous characteristics are also crowded back and replaced earlier 
by gerontic modifications similar to those which occur only in the 
senile stage of V. Konincki. ‘Thus these degenerative changes are 
shown to occur in what is properly the parephebic substage of V. 
pinguis. The history of the impressed zone accords with that of 
the other characters and may be seen in the figures to have been 
introduced as an acquired character dependent upon close coiling. 
It is not present in Triboloceras nor in the nepionic or ananeanic 
substages of the nautilian forms. It appears only after contact, and 
in other words is a contact furrow and its characteristics are deter- 
mined wholly by the moulding of the dorsum on the peculiar ven- 
tral surfaces which are encountered during growth. 
COLOCERAS GLOBATUM. 
NaUTILUS GLOBATUS, De Koninck (Cale. Carbon., Pl. xxxi). 
Pl, x, Figs. 1-14. 
The development of this species was partially described in my 
** Carboniferous Cephalopods,’’ second paper, fourth Ann. Rept. 
Geol. Surv. Texas, p. 447-451, but no figures were given and the 
genus Coloceras was then erroneously referred to the same genetic 
series as Coelogasteroceras. More extended study of both of these 
forms has shown me that the latter belongs to a distinct series. 
Coloceras globatum has the peculiar lateral flutes and characteristics 
of the Triboloceratidz in the nepionic and neanic stages, and the 
hollow ventral zone of the paranepionic substage, which led me to 
suppose that it belonged to the same genetic series as Coelogastero- 
ceras, may be accounted for equally well when C. g/odatum is referred 
to the Triboloceratide. Figs. 5 and 6, Pl. ix, of Vestinautilus Kon- 
znckt show that the broad, hollow, ventral zone of the ephebic 
stage becomes narrow and the abdomen is gibbous on either side of 
it in the anagerontic substage of this form. 
The similarity of the ventral hollow zone of the young of C. 
globatum may be accounted for, if it is supposed to be an accele- 
rated phylogerontic character. The only difficulty in the way of 
this assumption is the preéxistence of the lateral flutes in the neanic 
stage. I have, however, frequently seen similar examples of the 
unequal acceleration of characters and this is probably another of 
