DESCRIPTIONS OF LOWER LIAS FOSSILS. 417 



them are the fine concentric striae figured in Gabb's shell from the lower 

 part of the bed south of Sterretts mine. 



Entolium^ sp. (?) 

 Loc, Sailors canyon. 



In the same slab with the above is an imperfect cast of the interior, 

 showing the peculiar outline and teeth and apparently the extending 

 wings of an EatoUum. 



Gryphxa, sp. (?) 

 Loc, Sailors canyon. 



A small lot of this genus was found about one-half a mile distant from 

 the Sterretts Ammonites locality, but the species is not determinable. 

 They are supposed to belong in the upper part of the Ammonite bed. 

 Associated with them were the fragments and impression of an almost 

 entire valve of a delicately striated shell, and too other species of Pelecy- 

 poda, also not determinable. 



LOWER LIAS FOSSILS OF y EVA DA. 



Arnioceras nevadanum. 



Ammonites nevadanus, Gabb. Am. Jour. Conch., vol. v, 1869, pt. 6, pi. 3 ; 



fig. i, iv, pi. 16. 

 Arnioceras nevadanum, Hyatt. Gen. Ariet., p. 172. 



Loc, Volcano, 30 miles S. E. of Walkers lake, Nev. 



The reference of this species to the genus Arnioceras in my "Genesis of 

 the Arietida) " on account of the peculiarities shown by Gabb's figure 

 was correct. The young have a comi)ressed outline like that of Arnio- 

 ceras ceras, and it otherwise quite closely resembles that species. It is, 

 however, jirobably larger ; at least I have not yet seen any specimens of 

 ceras reaching so great a size as Gabb's specimen. The whorls of the 

 young in Gabb's figure are considerably broader than in ceras. 



The young during the nepionic stage are doubtless round and smooth 

 since in the ananeanic substage the abdomen becomes subacute, the keel 

 appearing in the metaneanic substage, and costse develop very rapidly 

 in the course of one-fourth of a volution into well-defined costations and 

 never have any tuberculations. The channels appear in the anej^hebic 

 substage on the third quarter of the fifth volution. 



The specimen has nearly nine whorls, and in Gabb's figure it is repre- 

 sented with the bottom part truncated, which is not the case in this 

 specimen, although in other respects it agrees exactly with the figure. 



