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vesents an “adaptive form, due to life in the egg, and does not represent 
any ancient ancestral genus, for none of the early cephalopods were 
shaped like this.” 
“With the formation of the first septum, the young ammonite has taken 
its place among the chambered cephalopods, and has become, for the time 
being, a nautiloid, although it is not possible . . . . to correlate it 
With “any special genus, = =. = “he first-septum > 3°. 2 sishneus 
tilian in character, but the siphuncle begins inside the protoconch with 
a siphonal knob, or caecum, and the protoconch itself is calcareous. These 
are two characters that the nautiloids even to this day, have never yet ac- 
quired. . . . . We have in this stage ammonite characters pushed 
back by unequal acceleration [telescoping], until they occur contempo- 
raneously with more remote ancestral characters.” 
There is no sign of an umbilical perforation as in the Nautilus, de- 
scribed above, a facet which again shows the degree of acceleration of 
these ammonites. 
With the second septum the ammonite characters are assumed. The 
shell at this stage is “distinctly goniatitic,”’ but also possesses characters. 
introduced by acceleration, that belong to later genera. The evidence 
indicating the goniatitic as well as later stages to be mentioned, is mainly 
the character of the suture lines. “At about five-eighths of a coil... . 
the larva has reached a stage correlative with the goniatites of the Upper 
Carboniferous.” This stage is quickly passed, and the goniatitic char- 
acters are lost and characters transitional to the ammonite stage make 
their appearance. “At one and one-twelfth coils the shell is transitional 
from the glyphioceran stage to what resembles closely the genus Nannites 
of the Trias.” In regard to this stage Smith says: “If it had not been 
said that this was a minute shell taken out of an older individual, any 
paleontologist would refer it without hesitation to the Glyphioceratide, 
and probably to . . . . Pronannites, of the Lower Carboniferous.” 
This stage lasts about one-half revolution. 
In the neanic stage, at one and seven-twelfths coils, the shell re- 
sembles very strongly Cymbites, or some related genus of the Lower Ju- 
rassic. The first signs of shell sculpture occur in this stage. ‘In the 
next stage the sculpture becomes stronger, and the shell assumes a de- 
cidedly aegoceran appearance. From two up to two and one-quarter coils, 
the shell resembles in most respects the stock to which Perisphinctes be- 
longs, and this is accordingly called the perisphinctes stage. During this 
