33 



The radula o{ lamellosa is quite narrow, and as a result the 

 aperture produced is minute. It is not known whether the 

 snails inject a narcotizing fluid in the attack upon their prey, 

 as is reported for some related forms. 



Some fishery biologists have been inclined to regard Thais 

 lamellosa as a predator upon the Olympia oyster {Ostrea luri- 

 da) of the Puget sound region, but the writer, in the course of 

 more than fifty year's experience, has never seen damage to 

 an oyster bed that could be ascribed to the activities of Thais, 

 The low concrete walls enclosing the shallow oyster dikes are 

 commonly encrusted with the small oysters in various stages 

 of development, and in the same situation one finds immense 

 numbers of Thais. In spite of this close association between 

 the oysters and the snails, no drilled oysters were to be found. 

 On the other hand, with the introduction of the Japanese oys- 

 ter drill {Tritonalia japonica) a great mortality of oysters took 

 place. Since Thais feeds mainly if not exclusively upon bar- 

 nacles and mussels, both detrimental to the oyster, the writer 

 would classify Thais as a highly beneficial organism, presum- 

 ably the only invertebrate **friend" of the oyster. 



ENEMIES OF Thais lamellosa. 



As has been indicated, the principal enemies of Thais are 

 various species of predatory birds, gulls, oyster catchers and 

 ducks. Colton (1916) has given a very detailed account of the 

 manner in which the gulls conduct their operations against 

 colonies of Thais lapilluSj both for their own food and that of 

 the nesting young. The same type of behavior on the part of 

 the birds is commonly seen on our western coast. In many 

 populations of T. lamellosa considerable numbers of the snails 

 appear in which the shells have been damaged and then re- 

 paired. The definitely notched appearance of the original 

 fractures was not due to mechanical injury, but was produced 

 by the beaks of birds, presumably gulls. This type of injury 

 is illustrated on Plate XII. 



