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



of the Tropites type. The ventral lobe is divided by a shallow siphonal 

 saddle ; there are usually two principal laterals and an auxiliary present ; 

 but in some species there is only one principal lateral, and the second must 

 be regarded as the auxiliary. 



The body-chamber is long, and at maturity shows a tendency to obso- 

 lescence of the ribs, also an egression of the whorl. 



Paratrofites seems to have departed less from the ances- 

 tral type than Trofites, and this is emphasized by the fact 

 that its young stages are much more similar to the mature 

 forms than in that genus, where great changes take place 

 in growth. It is not regarded as a radicle of the Tropitidas, 

 nor even as nearly allied to that radicle, but merely as a 

 highly specialized group that has preserved certain charac- 

 ters that must have been present in the primitive stock of 

 the Tropitidse. Paratrofites appears not to be any older 

 than Tropites; it is known in the Karnic stage of the 

 Upper Trias, in the Mediterranean region, in India, and 

 in California, and according to our present knowledge it is 

 entirely confined to that horizon. As is the case with TVc- 

 pites, it appears unheralded by local ancestors in all three 

 regions, so that its place of origin and its immediate ances- 

 tors are unknown. That the Tropitidae in the stricter sense 

 all came from a common origin can not be doubted, but at 

 present no genera are known in the Middle Trias that could 

 have given rise to this group. 



Paratropites is represented in the Karnic stage, zone of 

 Tropites siihbiiUatiis, of Shasta County, California, by two 

 species that seem to be identical with Alpine forms, P. sel- 

 lai Mojsisovics and P. dittmari Mojsisovics, as well as by 

 a large number of species nearly allied to Mediterranean 

 forms. 



Paratropites dittmari Mojsisovics. 



Plate XLVI, Fig. i ; Plate XLVII, Fig. i. 



1893. Tropites {Paratropites) dittmari, Mojsisovics, Cephalopoden der 

 Hallstatter Kalke, II, p. 245, pi. cxv, fig. 4. 



Involute, discoidal, laterally compressed. Whorls deeply embracing, and 

 deeply indented by the inner whorl. Sides flattened-convex, with abruptly 

 rounded umbilical shoulders, and rather gently rounded abdominal shoul- 

 ders. Venter narrow and arched, surmounted by a central keel with distinct 



