IS93-] 105 
[Hyatt. 
Altliougli the stjiges that siKH'oed the nejiioiiic vary exter- 
nally in different genetic series or phyla and in different forms of 
the same |)hylnni, so that they cannot be considered characteristic 
of the entire order of nautiloids, they are very significant when 
studied in more limited groups according to the comparative 
method of research employed in l)iopIastology. I have recently 
had occasion to use these terms in researches on Carboniferous 
cephalopods now publishing by the (Tcological survey of Texas, 
and those who care to follow this subject farther will find 
examples of the mode in which I have employed them in the next 
annual report of the geological survey of that state. It is only 
essential to say here that each term had its utility tested and was 
found essential to the accuracy of the descriptions of the stages of 
development before it was adopted. 
I have thus ascertained that among nautiloids of the Carl)<)ni- 
ferous the metanepionic whorl usually became a depressed elli|(se, 
that is, one Avith the transverse axis longer than the dorso-veiitral, 
anil ornamented with coarse longitudinal ridges, whether the 
shell was subsequently sniooth or remained ridged. The septa 
succeeding the first septum among nautiloids and attributable to 
the metanepionic stage have a large siphuncle compared with the 
ventro-dorsal axis, and this has been called the '■'■macrosij)honula." 
The macrosiphonula brings before the ol)server certain internal 
characteristics, which, although much altered, appear to liave 
been derived from the earliest known ancestors of the nautiloids, 
the Endoceratidae. The metanepionic stage is therefore in part 
in all forms very primitive in spite of the fact that in highly 
accelerated nautilian shells it is very much modified and also that 
most of its characteristics are derived from the more recent 
ancestors of its own ordinal or sub-ordinal, or family or even 
generic i)hylum, as is the case in beleninoids and aniiuonoids and 
among nautiloids. 
The paranepionic substage so far as I know does not carry any 
characteristics derived from a very remote ancestry but usually 
in nautilian shells points very definitely to some known or 
unknown cyrtoceran or gyroceran ancestor. This is broadly 
shown in the fact that in all of the more generalized forms of 
nautilian shells the three parts of the nepionic stage occur before 
the whorls touch. The external characteristics and form of the 
metanepionic and the whole of the paranepionic substage thus 
