Vol. ;o._ DEVELOPMENT OF TRAGOPHTLLOCERAS LOSCOMBI. 359 



Ussurites, the highest ammonites of the Lower Trias), began to 

 develop rapidly with the sue.ssi and sphcerophyllus groups of 

 Monophyllites, at the base of the Middle Trias. 



Nomisnwceras, which is erroneously regarded as the ancestor of 

 Monophyllites by Prof. Hang (1908, vol. ii, pt. i. p. SOU) and 

 Dr. Perrin-Smith (1913, p. 650), is a dwarfed, lateral development 

 off Glyphioceras, with extreme latumbilication setting in. 

 Popanoceras and Cjjelolobus, on the other hand, which are con- 

 sidered to he the ancestors of 3Io/toj)J/j/II/fr.s by Zittel (1910) 

 and Prinz (1904). apparently lead to Megaphyllites and Phyllo- 

 cladiscites : and we have already seen that a comparison of the 

 suture-development in MegapJiyllites with that of Monophyllites 

 does not reveal any connexion of JL^/aplij/Uites and Popanoceras 

 with the Monophyllitidae. The question of relationship can only 

 be settled definitely, however, when the ontosrenv of these Permian 

 and Triassic forms has been studied. 



The following is suggested as an improvement on the existing 

 classification : — 



Glyphioceratida : 



Thalassoceratidae : 



Dimorphoceras — Anthracoceras — Thalassoceras — Ussuria — 



Ussurites. 

 Phylloceratida : 



Moriophyllitidaa : 



Monoph yllites — Mojsvarites. 

 Pliylloceratidae : 



Discopliyllites — Pltylloeera* — Geyewcems — RhacophylliU 



Dasyceras — Scliistopltylloceras—Meneiili iniceras —Soicerbyc&nxs. 



Pleura canthitidae : 



Tragophylloceras — En pli yllites — ?Psilophyllitet> —Parapsilo- 

 ceras — Pleuracanihites — Eetocentrite*. 



In conclusion, I desire to express my best thanks to the 

 authorities of the British Museum (Natural History) for permission 

 to examine the material in their custody and to dissect certain 

 specimens ; to Prof. Paul Lemoine, of Paris, for information 

 regarding A. d'Orbigny's figured specimens: to a number of friends, 

 especially to Dr. Wyatt Wingrave and to Mr. J. Francis, F.G.S.. 

 for permission to examine their ammonites ; and to Mr. C. P. 

 Chatwin. for bibliographic assistance and for reading through the 

 manuscript. My especial thanks are due to Mr. W. I). Lang, who 

 has collected the material so admirably, and Avhose keen enthusiasm 

 for research anions the ammonites has greatly encouraged me in 

 the preparation of this paper. 



V. BlELlOUKAPHV. 



J. F. r.i.AKE (1892).— : The Evolution & Classification of tbe Cephalopoda, an 

 Account of Recent Advances' Proc. Geol. Assoc, vol. xii. pp. 275-95. 



W. Bkaxco i 1879). — ' Beitra<re zur Entwicklungsgeschichte der fossilen Cephalo- 

 poclen ' Pala?ontogrraphica, vol. xxvi, pts. 1 & 2, p. 25. 



