316 



resents an "adaptive form, clue 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 The first septum .... is nau- 



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 fact 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 X a unites 

 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 Glyphioceratidre. 

 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 Gymbites, 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 Perisptiinctes be- 

 longs, and this is accordingly called the perisphinctes stage. During this 



