UPPER TRIASSIC SPECIES. 121 



conclusion that it was not due to accidental distortion, it may be natural in 

 the form under consideration. 



It is quite similar, even in its elliptic form, to a compressed variety of 

 A. Batteni, Stoliczka (Mem. Geol. Survey of India, V, plate vi, figs. 1 and 

 1 a), figured by Dr. Stoliczka, from rocks of the same age in India. It is 

 even more strongly compressed, however, and has a proportionally smaller 

 umbilicus. Although it may possibly belong to the same species, it is far 

 more probable that it does not. Until its septa can be seen, of course its 

 generic relations must remain doubtful. It is not a true Ammonite, how- 

 ever, as the genus is restricted by the latest investigators of the fossil 

 Cephalopoda, but may be placed provisionally in the genus Arcestes until 

 its true relations can be determined from specimens showing the septa. 



Some months after writing the above, I received the following note in 

 regard to it from Professor Hyatt: 



''This species seems to be very closely allied to Arcestes Baonicus, Mojs. 

 (Jaln-b. Geol. Keichsan., Wien, XIX, 136, 1869). It is smooth and has no 

 keel, but is simply subangular on the abdomen, and has no knots on the 

 sides, as described in A. Baonicus. There are certain resemblances to Am- 

 monites glaucus which need comparison, and, when the septa are known, they 

 may prove more important than would appear to be the case." — (A. H.)* 



Locality and position. — Buena Vista Canon, South Fork, West Humboldt 

 Range; Upper Trias (St. Cassian beds). 



Arcestes Gabbi, Meek. 



Plate 10, figs. 6, 6 a, and 6 h. 



Arcestes Ausseeanus, Gabb (1864), Palseont. Cal., I, 25, pi. 3, figs. 16 aud 17 (not of 

 Hauer.) 



Shell compressed-subglobose, being rounded on the periphery and 



convex enough on the sides to present an elliptic profile view; volutions 



increasing gradually in size, each so profoundly enveloping all of those 



within as to leave only a very contracted, deep, almost cylindrical umbil- 



* Oa comparison with Laube's figures of Aimn, glaucus, Munster, our shell is seen 

 to be very similar in form, but its volutions are more embracing and more rapidly ex- 

 pand, while its umbilicus is consequently proportionally smaller. Of course the septa 

 as figured by Dr. Laube, unless made out from a very young shell, would show Amm. 

 glaucus to be very distinct from Ammonites proper. 



