Gkol.— Vol. I.] SMITH— GLYPHIOCERATID^. 109 



although on the type of Prionoceras, Goniatites helvaliamis 

 de Koninck, the first lateral saddles are angular. The only- 

 difference between the two genera is that Brancoceras is 

 compressed, high-whorled, almost discoidal, and very in- 

 volute; while Prionoceras is broad, low-whorled, and evo- 

 lute. Hyatt considers Brancoceras as the radicle of the 

 GJyfhioceratid<^, and traces the group from Anarcestes of 

 the Lower Devonian, through Tornoceras (Parodiceras) of 

 the Middle -Devonian. He admits the near relationship 

 between the two genera, but considers Prionoceras as the 

 link between the supposed radicle Brancoceras and Glyphi- 

 oceras. The genealogy of the Glyphioceratidcs, according 

 to Hyatt, is as follows : 



i Prionoceras-i-Cilyphioceras 

 Anarcestes-i-Tornoceras-i- Brancoceras <Miinsteroceras-i-Gastrioceras->-Paralegoceras 



fDimeroceras-«-Pericyclus 



Professor K. A. von ZitteP has recently merged Priono- 

 ceras in Brancoceras, not even giving subgeneric rank to the 

 former. But even though they may be nearly related, their 

 phylogeny justifies the separation. Both genera undoubt- 

 edly branched off about the same time from Tornoceras in 

 the Upper Devonian, but Brancoceras is not the radicle. 

 While it is possible, although not known, that Miinstero- 

 ceras may go through a Brancoceras stage, Prionoceras 

 does not, neither does Glyphioceras. Prionoceras comes 

 directly from Tornoceras, and in turn gives rise to Glyphio- 

 ceras. It seems likely, too, that some species of Gastrioceras 

 descended directly from Prionoceras by division of the 

 ventral lobe, while others may have come from Milnstero- 

 ceras. In any case, whether it came off from the radicle, 

 or through Milnsteroceras, Gastrioceras is a later branch 

 than Glyphioceras, not being certainly known below the 

 Coal Measures, and having its maximum in the Upper Coal 

 Measures; it therefore deserves to rank as an independent 

 genus. It also seems proper to retain Prionoceras and 

 Brancoceras with full generic rank, and Milnsteroceras as 

 subgenus under Glyphioceras. 



1 Grundzuege der Palaeontologie, 1895, p. 398. 



