118 PROCEEDINGS OF THE NATIONAL MUSEUM vol. los 



B. beringi, but there is so much variation, with all types of inter- 

 gradations between the typical and the var. kobelti, that it is impossible 

 to separate some of them. (Middendorff named his species after the 

 explorer Bering. Under the impression that the latter's name was 

 spelled with an "h," he originally wrote T. Behringii but later changed 

 it to T. Beringii and in a footnote (1851, p. 224) explained that he had 

 learned Bering spelled his name without an "h.") 



Typically, var. kobelti has a thinner shell, longer spire, shorter aper- 

 ture, and more curved canal than B. beringi. Also, var. kobelti has a 

 tendency toward 7 definite sides (pi. 12, fig. 6), whereas B. beringi is 

 not so angular (pi. 12, fig. 1) and the last whorl is more tumid than 

 in var. kobelti. 



The specimens from Point Barrow include t3'pical B. beringi, t3^pical 

 var. kobelti, and every possible combination of characteristics in 

 between. Some are seven-sided, others six-sided; some have promi- 

 nent ribs and concave sides; others have obsolete ribs and convex 

 sides; while in others the sides are almost flat. Dall's original de- 

 scription states: "The axial waves (they can hardly be called ribs) 

 of V. kobelti are feeble and irregular. . . ." Whether waves or ribs, 

 they are certainly not feeble in some of the specimens. In some the 

 spire is long and slender, with whorls increasing gradually in size; in 

 others it is short and the whorls increase rapidly (pi. 12, fig. 3). In 

 some shells the aperture is longer than the remainder of the shell (pi. 

 12, fig. 3); in others it is shorter; and in still others the aperture and 

 the remainder of the shell are about equally long. 



The variations in the nucleus are remarkable (pi. 12, cf. fig. 4 with 

 figs. 5, 6) : In some shells the nuclear whorls number only about 

 1.75, while in others there are more than 3 whorls; the diameter of 

 these nuclear whorls varies from relatively small to very large; the 

 whorls may increase rapidly in size or, in a nucleus of about 3 whorls, 

 they may all be approximate!}^ the same diameter. The length of 

 the nuclear whorls varies as much as the diameter and as much as 

 the length of the postnuclear whorls. 



In a specimen from Eluitkak Pass the spire is short (19 mm.), the 

 aperture long (30 mm.) ; there are two small, short, nuclear whorls, 

 and the postimclear whorls are short and tumid. Most of these 

 characteristics are like those of B. beringi, but the shell is thin, as in 

 var. kobelti. In a shell from 341 feet the aperture is 15 mm. long, 

 the remainder of the shell 15.5 mm., the 2.5 nuclear whorls are slightly 

 tapered (the first whorl being 5 mm. in diameter, the next, 6 mm.), 

 and the postnuclear whorls increase gradually in size. In stdl another 

 shell (medium thin) from 522 feet, the aperture is 22 mm., the re- 

 mainder of the shell is 23.5 mm., the 3+ nuclear w'horls are very 

 large and long and are approximately equal in diameter; the first 



