EVOLUTION OF FOSSIL CEPHALOPODA. 253 
descent; Glyphioceras goes through distinctly the stages 
from Anarcestes of the Devonian, through Zornoceras 
and Prionoceras, finally stopping in the Glyphioceras stage. 
Schloenbachia hastens through'the Anarcestes, Tornoceras, 
and Prionoceras so that they are hardly recognisable, 
and gets to be a Giyphioceras even in its middle larval 
stage, goes through two more goniatite stages, and 
several ammonite stages before it becomes a Schiloen- 
bachia. 
DEVELOPMENT OF GLYPHIOCERAS. 
Glyphioceras in its development does not show the 
Bactrites (Plate V, Fig. 7) and Mimoceras (Plate V, Fig. 
8) stages, so these must be studied in lower forms; but 
from the Axarcestes stage up they are sharply defined. 
It begins life as a protoconch or embryonic shell while 
undoubtedly still in the egg; this (shown on Plate I, 
Figs. 1-5) corresponds to the primitive cephalopod. At 
the beginning of its larval stage the animal left the 
protoconch, built up the first body chamber, and cut off 
the embryonic part of the shell by the first septum 
(Plate I, Figs. 6 and ro, Plate IV, Fig. 1,1); at this stage 
the shell is analogous to the primitive nautiloid, and it 
is called in Hyatt’s nomenclature ananepionic. With 
the second chamber the young shell becomes an ammo- 
noid, and corresponds to the genus Axarcestes of the 
Lower Devonian; this is shown on Plate I, Fig. 6, and 
on the second and third septum of Fig. 9, also Plate IV, 
Fig. 1, second and third sutures. On Plate IV, Fig. 7 
shows for comparison the septa of Azarcestes subnautilinus 
Sandberger. At the fourth suture the shell is transi- 
tional to Zornoceras of the Middle Devonian, Pilate I, 
Fig. 9, shows the beginning of the Zorzoceras stage, 
which lasts through the sixth chamber, as shown on 
Fig. 12, and on Plate IV, Fig. 1, at the fourth and fifth 
septa. For comparison the development of the septa of 
