i6 



VARIATION IN THAIS LAMELLOSA 



Throughout the range of this species, which extends from 

 the Aleutian Islands to Monterey on our western coast, there 

 is to be found an immense number of populations which paral- 

 lel if they do not exceed the profusion of local races presented 

 by the related species Thais lapillus inhabiting the Atlantic. 



These populations of Thais present a series of problems. 

 To the taxonomist they are of interest because of the difficulty 

 of fitting them into the traditional descriptive pattern. Un- 

 like the tree-snails of the Hawaiian Islands, which differ main- 

 ly in their color pattern, the variants of the lamellosa complex 

 differ widely in the size of the shell, its proportions and sculp- 

 ture, as well as in coloration. To provide each one of these 

 distinctive local races with appropriate latinized subspecific 

 names, as was done with the achatinellids, would be a task of 

 formidable proportions. 



To the ecologist the group should be of interest because of 

 the conspicuous place they occupy in the biota of the inter- 

 tidal zone. Living as they do mainly on barnacles, they are 

 provided with an ample and quickly replenished food supply, 

 while their compact shell protects them from most ordinary 

 enemies. There is the additional ecological interest in the 

 question as to what extent the visible differences among the 

 several local races may be due to environmental conditions, a 

 much mooted problem. 



To the student of microgeographical speciation as a factor 

 in the evolutionary process, these Thais forms present us with 

 an outstanding example. 



Since the basic characters are obviously due to the unequal 

 dispersal of the genie system, it seems probable they would 

 provide interesting material for breeding experiments, a found- 

 ation for which has been provided in the thorough work upon 

 the genetics of Thais lapillus by Staiger (1955). 



