35 



The forms most often met with that excavate the shells 

 are boring sponges and annelids of the Polydora type, but these 

 are infrequent and seem to do no serious harm to the snails. 



The larvae of several species of trematode worms have been 

 reared from the snails (Miller); the adult forms are presum- 

 ably parasitic in their vertebrate predators. 



Certain species of minute algae, said to belong to the genera 

 Gomontia and Plectonema (Moore, 1938) etch away the limy 

 surface of the shell, and often obscure the more superficial 

 sculptural details. 



In a few instances specimens have been found in which the 

 shells of the snails were covered with a coating of an alga 

 delonging to the genus Lithotharnnion. 



TAXONOMIC INTERPRETATION 



The immense number and highly localized character of the 

 populations of Thais lamellosa brings into sharp focus the prob- 

 lem of the adequate taxonomic treatment of these and other 

 similar infraspecific demes. 



The treatment of this problem by Dull (1915), who simply 

 selected four divergent forms which he characterized as 'Vari- 

 eties", is obviously quite inadequate and outmoded. 



These demes are obviously of the type to which the status 

 of subspecies is commonly assigned. Some authors, as in the 

 case of the achatinellid fauna of Hawaii dealt with by Welch 

 (1942), have introducded large numbers of latinized subspecific 

 names. It seems unfortunate that the literature should be bur- 

 dened in such cases by names coming within the scope of the 

 laws of priority. It appears to the writer that the trend in 

 taxonomic procedure is definitely against this practice in deal- 

 ing with highly polytypic species. 



The use of the term ** form*' or "forma" has been utilized 

 by some authors to designate these variant populations, but 

 this usage suffers under the handicap that it has been used in 

 other connections, so that it is not sufficiently distinctive. 



