8 



In recent years there has been inaugurated an intensive 

 study of animal populations in an effort to determine the rela- 

 tive importance of genetic, ecological and spatial factors in 

 bringing about the evolutionary differentiation of organisms. 

 Observations in the field have been supplemented by breed- 

 ing experiments, physiological studies, statistical analyses and 

 genetic interpretations. The literature in this field has already 

 become quite extensive: it has been thoroughly summarized by 

 Dr. Ernst Mayr (1949), with emphasis upon spatial and other 

 phases of isolation as factors in the evolutionary process. 



The present paper is designed to place on record some of 

 the local races of Thais lamellosdy which is highly polytypic 

 and is distributed along the Pacific Coast from California to 

 the Aleutian Islands, exhibiting an endless diversity of size, 

 coloration and sculpture. 



The writer first became interested in the marine snails of the 

 Thais group at the time he entered the University of Wash- 

 ington as a student in 1894. At that time a group of persons 

 known as the Young Naturalists Society maintained a meet- 

 ing place and a museum in a small frame building standing 

 upon the campus of the university, which at that time was 

 located in downtown Seattle. The membership included sev- 

 eral persons interested in ** conchology", now known under 

 the more dignified title of " malacology'*. They had accumu- 

 lated a considerable collection of Thais material, but had been 

 baffled in their attempts to classify them when they found 

 the various forms shaded into one another by insensible gra- 

 dations. The significance of the localized races of these forms 

 apparently had not been realized. 



With the establishment of the Puget Sound Marine Station 

 (later renamed the Oceanographical Laboratories) under the 

 auspices of the University of Washington, beginning in 1901, 

 the writer was brought in contact with the rich marine fauna 

 of the San Juan Islands. This interesting archipelago located 

 in the Gulf of Georgia includes a large number of rocky is- 

 lands of various sizes, and many reefs both emergent and 

 non-emergent at low tide levels, and since the larger islands 



