430 A. HYATT — TRIAS AND JURA IN THE WESTERN STATES. 



Amusium aur avium , Meek. lOZH^^ 

 Log., six miles from Copperopolis on road to Sonora and grade to 



Angels creek. 



A shell probably of this species occurs at this locality, but it is not 

 perfectly symmetrical, as in Meek's figure of the same species. 



Aucella erringtoni, Meek. 

 Variety, arcuata. 



Aucella erringtoni. Geol. Sur. Cal., vol. I, appendix, pis. 1, 2a (not figs. 



3,4,6). 

 Loc, south bank of Tuolumne river at Mofi'at's bridge ; Stanislaus river 



near canyon opposite Bear creek, and six miles from Copperopolis on 



road to Sonora and grade to Angels creek. 



This variety represents the extreme form and is arcuate in the left 

 valve with a very prominent umbo. The striations are less decided 

 than in Aucella elongata. There are a few shells which are apparently 

 smooth, while most are striated as in Aucella elongata. The task of sepa- 

 rating this from other varieties by the characteristics of the relative pro- 

 portions of the left valve to the right and other characters, such as the 

 relative prominence of the umbones in both valves, shape of the hinge 

 line in the right valve, and so on, is impracticable on account of the 

 compressed and more or less distorted condition of every fossil. It is, 

 obviously a near affine of Aucella pallasi, sp. Keyserling,* as figured 

 and described by Lahusen from the zone of Cardioceras alternans in 

 Russia, in so far as the general shape and striations are concerned, 

 and Keyserling's original drawings and descriptions of Aucella 'pallasi 

 give longitudinal striations and a form of shell so close to this that with- 

 out the right valve and hinge line they would be considered identical. 

 With the complete information given by the drawings of the latter, how- 

 ever, it becomes apparent that they are not both referable to the same 

 species. The hinge line of the right valve of the arcuata is more like 

 that of mosquensis, while the general shape of the shell alone is like that 

 o^ pallasi mosquensis, from the Volgian or middle part of the Upper Jura 

 in Russia. 



Aucella concentrica, Fischer,* has a right valve and general outline 

 closely similar and possibly identical with arcuata. The left valve, al- 

 though not completely shown, appears to be similar to that. The same 

 species and the stout, rotund variety shown in figure 6 has its counter- 

 parts in some specimens from the last locality given above which have 

 no striae. The outline of the hinge of the right valve need only be com- 



* Reise in Petsehoruland, pi. 16. 



