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



the base than at the top, and without bordering furrows. The outer whorl 

 is one-half the diameter of the shell, and the breadth is one-half of the height 

 of the whorl. It is indented to one-third of the height by the inner volution, 

 and conceals three-fourths of that volution. 



Surface ornamented with numerous fine, but distinct, sickle-shaped ribs, 

 that curve backward on the flanks and forward on the shoulders to the base 

 of the keel, where they become obsolete. These ribs are either single or 

 dichotomous, the division taking place nearly half way up the fianks. The 

 ribs are rounded, low, and narrower than the intercostal spaces; there are 

 about sixty to a revolution on the mature shell. In addition to these there 

 are fine spiral lines that show distinctly on the cast as well as on the shell. 

 Around the umbilicus there is a row of small knots, the remnant of coarse 

 umbilical ribs in the Tropites stage of growth. 



The septa are ammonitic, but comparatively simple, lobes and saddles all 

 digitate, but not deeply so. External lobe divided by a shallow siphonal 

 saddle into two short branches. First lateral lobe broader and deeper; 

 second lateral less than half the size of the first; auxiliary shallow and com- 

 posed of two or three indentations on the umbilical shoulder. The anti- 

 siphonal lobe is flanked by three internal laterals. 



The young of E^itomoceras sandlingense are robust, and 

 not discoidal, resembling Paratropites; they can, however, 

 be distinguished from that genus by their sharper venter. 

 In the earlier stages the sculpture is much rougher than at 

 maturity, resembling that of Tropites; but in EtUomoceras 

 sandlingense the ribs appear before the keel, at the diameter 

 of about one millimeter, while the keel does not appear until 

 a diameter of two and seven-tenths millimeters is reached. 

 In all species of Trofiies and Paratro^iies examined by the 

 writer the keel develops before the lateral ribs. From the 

 development of this species it is clear that Paratrofites 

 connects it with Tropites. The earlier larval stages are 

 like Gastrioceras of the Carboniferous, and probably in- 

 dicate derivation from that genus. 



The Californian specimens show as much variation as do 

 those of the Alps, there being no constancy in the size and 

 number of the ribs. 



Mojsisovics assigned this species to Hyatt's genus 

 Eiito7noceras, which is nearly allied to Hungarites under 

 the Ceratitoidea ; but all its characters point to an origin 

 from the Tropitidee. 



Horizon and locality. Upper Trias, Karnic stage, zone 

 of Tr of lies siibbullatus, Brock Mountain, divide between 



