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Dr. H.Coltonintwo papers, one published in I9i6the other 

 in 1922, contributed some interesting observations upon the 

 possible origin of the local races of Thais found upon the coast 

 of Maine in the neighborhood of Mt. Desert Island, in which 

 area there is a tidal movement averaging about ten feet. 



In his first paper (1916) Colton dealt primarily with the 

 phenomenon of coloration as displayed by these snails. For 

 purposes of comparison he had available 12,000 specimens 

 derived from 67 separate localities. He subjected this material 

 to statistical analysis to determine whether any relation ex- 

 isted between the prevailing environmental conditions and the 

 coloration of the shells. 



Among the conclusions reached by Colton was the sugges- 

 tion that, while the variations in color exhibited by the local 

 races were primarily determined by the constitution of the 

 germ cells and hence basically hereditary, there was a low- 

 pressure selective action functioning through the activities of 

 predators utilizing the snails for food. He found evidence that 

 sea-gulls prey extensively on Thais, since considerable quan- 

 tities of the shells were found upon areas frequented by the 

 birds. He assumed that in a population that was more or less 

 protectively colored, those individuals that were conspicuous 

 would be most likely to be seen and devoured by the gulls, or 

 by predatory fishes while the intertidal area was covered with 

 water; thus in areas where the rocks were covered with barna- 

 cles dark colored specimens would be conspicuous, while on 

 areas where mussels predominated, pale colored individuals 

 were more apt to be seen and eliminated by predators. 



Colton noted that the problem of coloration is complicated 

 when the bulk of the population in a local race includes not 

 only individuals with solid coloration, but those with inter- 

 mediate shades and various types of banding. 



In regard to sculpture Colton states that he found both im- 

 bricated and smooth varieties in protected muddy bays, which 

 led him to the conclusion that sculpture was determined by 

 heredity rather than by environmental factors. 



