Geol.-Vol. I.] SMITH— LYTOCERAS AND PHY LLOCEK AS. 149 



diameter of 35.00 mm. ; these do not agree perfectly with 

 those figured by Gabb, but in the photograph there was no 

 chance for error as in free-hand sketching. The number 

 and position of the internal lobes are merely indicated by a 

 dotted line, as the details could not be made out. 



Table of Stages of Growth. 



Conclusion. 



In the preceding pages it has been shown that Lytoceras 

 in its development goes through the following stages : phy- 

 lembryonic, protoconch representing some unknown cepha- 

 lopod; ananepionic, representing some Silurian nautiloid; 

 metanepionic, already an ammonite, and corresponding to 

 Nannites, or to some other early genus of the Cyclolobidas ; 

 paranepionic, at first corresponding to the sculptured group 

 of Nannites, and later transitional to the earlier members 

 of the Lytoceratidae ; neanic, analogous to that group of 

 Monophyllites with two lateral lobes, and transitional to the 

 adult characters of Lytoceras at diameter of 7.00 mm. 



Phylloceras begins life just as did Lytocei-as, coming from 

 the same remote ancestor, and agreeing with that genus in 



