122 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



monites of the Trias. Glyfhioceras in its ontogeny goes 

 through the following stages: phylembryonic, protoconch, 

 representing the primitive cephalopod; ananepionic, Silu- 

 rian nautiloid; vaoX'^n^-^xonxo., Anarcestes oi Lower Devon- 

 ian; paranepionic, Tornoceras of Middle Devonian; neanic, 

 Prionoceras of Upper Devonian and Carboniferous, show- 

 ing gradual transition through ana-, meta-, and paraneanic, 

 and a gradual change from Prionoceras to Glyfhioceras in 

 the late adolescent and early adult stages. Prionoceras is 

 undoubtedly the family radicle, and Brancoceras is a side- 

 branch, since Glyphioceras does not go through any stage 

 corresponding to the latter genus. Gastrioceras comes from 

 Prionoceras (through Miuisteroceras )hy somewhat narrow- 

 ing the whorl and division of the ventral lobe. Glyphioceras 

 comes directly from Prionoceras by narrowing the umbilicus 

 so as to conceal most of the inner whorls and by division of 

 the ventral lobe. 



The division of the subfamily Glyphioceratidce into Bran- 

 coceras, Prio7ioceras, Pericyclus, Glyphioceras, (subgenus 

 Mtinsteroceras), Gastrioceras, Paralegoceras, is quite proper 

 for phylogenetic reasons. 



According to Steinmann the Ceratitidce of the Trias are 

 descended from Gastrioceras, and the Tropitidce from Peri- 

 cyclus, but neither of these groups goes through stages of 

 growth corresponding to these genera. Tropitcs does, 

 however, go through a Prionoceras stage, and later it resem- 

 bles closely Gastrioceras, but it already has the Tropites 

 keel before the ventral lobe is divided. It then descends 

 from the Glyphioceratidcs , but directly from the radicle and 

 not through any modified form. But it is quite likely that 

 some of the genera assigned to the Trofitidce do descend 

 directly from other members of the Glyphioceratidce. 



LELAND STANFORD JUNIOR UNIVERSITY, 

 CALIFORNIA, 



October, 1897. 



