Gbol— Vol. I.] SMITH— COMPARATIVE STRATIGRAPHY. 395 



This species is nearly related to Tro^ites dilleri Smith, 

 sp. nov., but differs in its more compressed whorl and nar- 

 rower umbilicus. It differs from Trofites subbullatus in 

 its greater lateral compression, narrower umbilicus, and 

 weaker sculpture. 



Horizon atid locality. Upper Trias, Karnic stage, zone 

 of Tro-pites subbullatus, Shasta County, California, Brock 

 Mountain, on the divide between Squaw Creek and Pitt 

 River, six miles northeast of the Bully Hill Mine. This 

 species was first found in the Tyrolian Alps, in the same 

 horizon, and associated with the same fauna. 



Genus Paratropites Mojsisovics. 



1893. Paratropites Mojsisovics, Cephalopoden der Hallstatter Kalke, Bd. 



II, p. 184. 

 1896. Paratropites Mojsisovics, Beitr. Kennt. Obertriadischen Cephalopo- 



den-Faunen des Himalaya, p. 611. 



Mojsisovics gave the name Paratropites to what he con- 

 sidered as a subgenus under Tropites, and did not name 

 any type, nor mention any species in the diagnosis. The 

 first species described by him under this group, Paratro- 

 pites bidichotomus Mojsisovics,^ would then, according to 

 usage, become the type, but it is neither characteristic, nor 

 well known. The commonest and best known species of 

 the group, P. saturnus Dittmar, would serve much better 

 as the basis for the generic diagnosis, and this form, along 

 with P. sellai Mojsisovics, must have been in the mind of 

 the author as the prototype of the genus. 



The form is laterally compressed, deeply embracing, and deeply indented 

 by the inner whorls. The sides are flattened-convex, venter narrow, and 

 the whorls are usually higher than wide. The umbilicus is narrow, the inner 

 volutions usually being concealed. Umbilical knots are present on most 

 species, and from these dichotomous ribs run with gentle forward curve up 

 the flanks, and bend forward on the abdominal shoulders. On the venter is 

 a distinct central keel, usually with furrows on each side, at which the lateral 

 ribs end. This keel is smooth, and not crenulated by the ribs. No spines 

 occur, and knots are known only on the umbilicus. Constrictions have not 

 been observed on any of the numerous species of the group. 



The septa are ammonitic, but not deeply digitate; they are dolichophyllic 



1 See Bibliog. 23— II, p. 234, pi. cxxvii, fig. 11. 



