440 PROCEEDINGS OF THE ACADEMY OF [June, 



on some varieties of thais lapillus in the mount desert 

 region, a study of individual ecology. 



by harold s. colton. 

 Introduction. 



In this study an attempt is made to correlate some of the many 

 color varieties of Thais (Nucella, Purpura) lapillus with the condi- 

 tions under which the animal lives. The study is based on field work 

 carried out in the neighborhood of Mount Desert Island, Maine, in the 

 summer of 1915. Over 12,000 snails were collected from sixty-seven 

 localities, sorted, and the variations tabulated. These tables were 

 then compared with the environment of the snail. 



With respect to Thais there is a very general belief that color is 

 correlated with the color of the environment. Cooke (1895) cites a 

 locality in Cornwall where striped forms are found on striped rocks. 

 Blaney (1904) reports yellow forms were found to predominate on 

 the yellow granite rocks of Yellow Island, a small island in French- 

 mens Bay on the Maine coast. On account of the great variation 

 of Thais and the apparent predominance of one variety in a given 

 locality, a study of the variations might throw light on some of the 

 ecological factors of the sea beach. 



Life History of Thais. 



Thais (subgenus Nucella or Purpura) lapillus is a carnivorous 

 prosobranch mollusk. It feeds almost exclusively in this region on 

 the mussel, Mytilus edulis, and the barnacle, Balanus balanoides. 

 The former it attacks by boring a hole in the shell about 1 mm. in 

 diameter, devouring the soft parts by means of its long flexible 

 proboscis. The barnacle is eaten in much the same manner, the 

 hole being drilled through one of the scutes. Not only do they 

 sometimes attack the periwinkle, Littorina littorea, but will try to 

 bore through the shell of one of their own kind. Although many 

 shells show scars, there is no evidence, however, that many are 

 destroyed in this way. 



The descriptive ecologist has neglected the Atlantic coast north 

 of Cape Cod. King and Russell's classification for the coast of 

 Scotland will not hold for this region. Some day, if some one else 



