69 



8. During the Pleistocene far-reaching changes in the level 

 of the ocean took place, as well as changes in the elevation of 

 the land, both eustatic and tectonic, which in combination 

 with the advance and retreat of the great continental glaciers 

 over the northern world, must have profoundly affected the 

 distribution and ecological adjustments of intertidal forms. 

 These factors undoubtedly had a profound influence in deter- 

 mining the character of the local races o^ Thais ^nd other inter- 

 tidal forms with limited powers of dispersal. 



9. The chromosome number in Thais lamellosa has been 

 determined by Dr. H. Staigertobe 35, but the relationship of 

 these elements to the variations found in the structure and 

 coloration of the shells cannot be determined without compre- 

 hensive, controlled breeding experiments. 



10. To avoid the use of an indefinite number of trinomials, 

 the writer has adopted a suggestion offered by Dr. J. Go* ^on 

 Edwards that such products of microgeographic isolation be 

 termed "morphs", pinpointing as closely as possible the local- 

 isation of the several populations. 



11. Fifty-three morphs, designed to illustrate the extensive 

 range of variation exhibited by the local populations of Thais 

 lamellosa J are figured and discussed. 



