48 



indicated by the morphs shown in Plates liii-lv, lxx, lxxii. 

 This group is well represented in British Columbia, (Plates 

 XLVi, Lii), and extends in a modified form into some areas 

 in the San Juan Islands (Morphs 30, 32, Plates XLv, xLvii). 

 This form does not appear to have any well defined repre- 

 sentatives in the Puget Sound area, although a tendency to 

 develop an elongated spire appears in many populations wirh- 

 io the entire range of the species. 



The populations occurring in the coastal region extending 

 from Santa Cruz, California, to Cape Flattery, do not exhibit 

 the diversity of sculpture and coloration seen in the northern 

 forms, possibly because they have not been subjected to the 

 disturbing effects of race-crossing with genetically different 

 alien populations. 



Although the amount of material available for study from 

 the Aleutian Islands is unfortunately very limited, the writer 

 is inclined to think this section also contains populations that 

 are genetically conservative, judging by Morphs 48 and 49, 

 shown on Plate lxxi, and beach worn specimens from Adak 

 and Unalaska Islands. Material from Kodiak Island, Morph 

 51, Plate LXXI 1 1, appears to be of an intermediate type. 



The only material available from the Kuriles is a few shells 

 from Etoro Island, Morph 52, Plate xxxi 11, which appear to 

 be very similar to the forms of lameltosa found in the Aleutians, 

 and the writer has provisionally placed them with this species. 



It is needless to say the writer has had available for study 

 only a few of the innumerable populations of Tbais lamellosa 

 that inhabit the great range of this species, and of these it has 

 been possible to include but a few within the limits of the 

 present paper. 



The number of specimens of the several morphs available 

 for examination has varied from a handful to several hundred. 



In selecting shells for illustration the writer decided to util- 

 ize mainly the dorsal surface, since this gives a clearer view 

 of the characteristie sculpture and color pattern. 



