228 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



in Alaska,' British America,- and in varions parts of Califoruia.' In the latter region 

 the first-discovered examples were referred to the genera Inoceramua and Lima, re- 

 spectively, and their relation to the AuceJIax of the eastern hemisphere was not then 

 suspected. 



Shells of this genus have been found at various other localities and have been 

 referred to by various authors in their publications, but the foregoing references are 

 sufficient to indicate the wide geographical and the interesting circumpolar range of 

 the genus. 



While the distinguishing generic features of the shells which have been found at 

 all these widely separated localities in the northern hemisiihere are constant, the range 

 of variation in subordinate features, especially size and shape, is so great that no less 

 than nine specific and several varietal names have been proposed by different authors 

 who have studied them. The figures on the accompanying plates have been prepared 

 to show the extremes of the variations which have been observed and to illustrate the 

 principal forms respectively which have been selected as types of the proposed species. 

 If only those forms to which the respective specific names have been applied had ever 

 been linown, the real specific identity of each might not have been questioned. For- 

 tunately, however, Aucella having been a gregarious molluslc, great numbers of speci- 

 mens have usually been found wherever any have been discovered, except at the New 

 Zealand, Brazilian, and Indian localities. Consequently, so large a number of inter- 

 mediate varietal forms have been found that I do not hesitate to express the opniiou 

 that none of the proposed species can be clearly diagnosed from the others, nor to treat 

 as a .specific unit all the forms referred to, with perhaps the exception of the Indian, 

 Brazilian' and New Zealand examples. 



It frequently happens that all or the greater part of the specimens found com- 

 mingled in any given layer agree closely with some one of the recognized specific 

 forms ; and it is also true that two or three of those forms are often found commingled 

 in one and the same layer. It thus often happens that a collection of these shells 

 made at one locality or in one neighborhood is found to contain representatives of more 

 than one, and .sometimes of the greater part, of the forms which have been recognized 

 as species by different authors. These representative forms liave usually been .selected 

 by authors for reference and illustration, while little mention has been made of the 

 intermediate forms. Tliat the foregoing statement is correct appears from the pub- 

 lications of the various authors referred to, and it also accords with my own obser- 

 vations upon the collections that have been made in North America. 



In view of the facts just stated, the conclusion seems to be necessary that all the 

 forms of Aucella which have yet been discovered, especially those of the northern hem- 

 isphere, have so close a genetic relationship with one another as to hardly exceed the 



1 E. EichwaU: Geognost.-palaeont. Beruerljiuigeu iiboi- die Halbiusel Maiigisclilak und ilie aleut- 

 ischen Inseln, pp. 185-187, PI. XVII, Figs. 1-17; P. Fisclier: Voyage a la cote uord-ouestde l'Ani(?rique, 

 par M. Alpli. Piuiirt, pp. 3:i, PI. A, Figs. 4 and o; C. A. Wliito: Bui!. U. S. Geol. Survey No. 4, pp. 10- 

 14, PI. VI, Figs. 2-12. 



-J. F. Wliiteaves: Proc. Traus. R<>y.al Soc. Can.ada, vol. 1, l^S'i, p. 84. 



^W. M. Gabb: Geol. .Sinvey California, Paleontology, vol. 1, 18fi4, p. 187, PI XXV, Fig. 17;'.; 

 ibid., vol. 2, 18G8, p. 194, PI. XXXI, Fig. 92; Proc. California Acad. Nat. Sci., vol. 3, 1885, p. 173; F. B. 

 Meek: Geol. Survey California, Geology, vol. 1, 1865, p. 479, PI. I, Figs. 1-5; C. A. White: Bnll. U. S. 

 Geol. Survey No. 15 ; G. F. Becker : Bull. U. S. Geol. Survey No. 19. 



