560 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.49. 



developed specimens of lamellosa there is an obscure tliickening on 

 the middle of the pillar. Well within the aperture in this species, 

 when weU developed, is a group of three (or occasionally four) teeth 

 separated by a marked gap from the posterior sinus of the aperture, 

 and by a less conspicuous gap from two more or less dentiform nodu- 

 lations near the constriction at the proximal end of the canal. Many 

 apparently weU-developed individuals, however, show no trace of 

 denticulation. For a long time it was supposed that N. lamellosa 

 was the only west coast species developing teeth, but Miss Bertha M. 

 Challis by careful search has found individuals of other species which 

 also do so. As a general rule, however, it may be stated that the 

 development of teeth in these northwest coast species is much less 

 constant than in the North Atlantic N. lapillus. 



The coloration of the shell varies in all the species. In most 

 specimens of lamellosa it is uniform over the entire individual and 

 ranges from pure white through various shades of yellow and yellowish 

 brown to a very dark brown. Specimens from quiet water are fre- 

 quently of a gray or greenish gray from an algal deposit which when 

 removed shows the true color of the shell. Some specimens have a 

 white band at or shghtly below the periphery, but any breaking up 

 of the other colored areas by additional white spiral bands is extremely 

 rare. 



This species never shows flammulation or bandmg of a darker or 

 different color. The margin of the aperture is generally pale, the 

 throat darker, brownish, or purplish brown in dark specimens; white 

 or slightly yellowish in white specimens. 



In N- canaliculata the range of coloration is about the same, except 

 that when banded there are usually two white bands, one near the 

 periphery and one on the base, and the resulting brown bands are 

 frequently broken up into patches or flammulations by gaps of paler 

 or whitish color. The outer lip is usually crenulated at the edge by 

 the exterior sculpture, and the interspaces between the spirals are 

 more or less reticulated by close-set axial elevated lines. The pro- 

 duction of teeth in this species is rare; when present, following a 

 posterior smooth space, there is a continuous line of eight or nine 

 small teeth to the begmning of the canal. In N. limn, the color charac- 

 teristics are much the same as in N. canaliculata, though it is rarely 

 flammulate ; but, even m the heaviest and most caUous adults, I have 

 not been able to detect any trace of denticulation in the aperture. 



In N. emarginata the most conspicuous feature, after the nodulation 

 of the spiral bands, is (except in unicolored specimens) the presence of 

 narrow, usually dark-brown bands between the lighter colored, 

 usually white, major spirals. None of the other species has this 

 feature. While the nodules are sometimes subspinose, there is never 

 any prominent axial lameUation. The pillar is conspicuously con- 



