232 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



Figs. .■$, 4, .and .'>. Copies of Gabb's subsequent figures of AiicrUa Piocliii (Geol. Survey California, 

 PalaiontolDgy, vol. 2, PI. XXXII, Figs. 92, 92o, and 926). 



FiG.s. 6, 7, 8, 9, and 10. Copies of Meek's figures of AuceUa Erringtoiiii {Lima Erringtonii Gabb) 

 (Geol. Survey Califoruia, Geology, vol. 1, Figs. 1, la, 2, 2a, and 5e). The radiating lines sbown on thise 

 specimens seem to Lave been somewhat exagger-ited by lateral pressure. 



Figs. 11, 12, 13, 14, and 15. Copies of the author's figures of specimens from Alaska, published in 

 Bull. U. S. Geol. Survey No. 4, PI. VI, Figs. 2, ."?, 8, 9, and 10. 



Figs. 16 and 17. Tt^o views of a remarkably ventricose left valve from the Knoxville division of 

 the .Sh.asta group near Knoxville, Cal. 



Figs. 18 and 19. Lateral views of two left valves from the Kuoxville division of the Shasta group 

 near Knoxville, Cal. These examples have suffered no lateral pressure, but the radiating lines have 

 been made a little too distinct by the artist. 



Fig. 20. A right valve from the same locality. 



Fig. 21. A left valve from Washington Territory, collected by Prof. Thomas Condon. 



These figures of North American specimens oi AiiceUa show, if possible, a greater 

 range of variation than do the figures given on PI. III. The forms known by the 

 specific names of eonccntiica, 2)allasii, anil crassicollis, respectively, are readily recog- 

 nizable among these figures of American Aucellas. There is, however, one form 

 among them which has ai)i)arently not been recognized outside the limits of North 

 America, and yet it is probable that it exists elsewhere. Figs. 10 and 17 represent 

 an extreme example of this form or variety from California and Figs. 14 and 15 repre- 

 sent a less pronounced exam[)le from Alaska. On the other hand, the form which 

 TuUberg figures as A. mosquensis, of which Figs. G, 7, and 8, PI. Ill, are copies, 

 does not appear among the North American forms which are here figured, and it is 

 probably rare in North American strata. 



Figs. 4, 13, and 21 may be taken as representatives of the form A. crassicollis, 

 and yet in each case the specimens represented by these figures were found com- 

 mingled and embedded with other forms. Figs. G, 7, 8, 9, and 10 are apparently 

 referable to the form .1. pallasii, as represented by Fig. 9, on PI. III. Figs. 18, 19, 

 and 20 ought probably to be regarded as varieties of that form, although there seems 

 to be quite as much reason for referring them to A. mosquensis. 



The radiating lines which appear upon some of these figures, as well as those of 

 some European exam i)les, are oftener seen upon the form .4. ;>rt7/rt.s/i than upon the 

 other forms; but such markings are not exclusively confined tOj,any one form. There 

 is also much difference observable in the strength of the concentric markings of all 

 the forms; but this cannot be regarded as even a varietal character. Many of the 

 specimens a])pear unnaturally smooth, because of the fact that a large part of the 

 examples discovered are casts of the interior of the shell, the test itself having been 

 destroyed or removed. 



