XX11 COLOR PATTERNS. 



I have elsewhere noted that in Liguus some forms show 

 an extremely interesting change in the pattern, whereby the 

 dark and the light markings exchange places, as in a photo- 

 graphic negative, without other noticeable change in the shell. 

 An entirely similar exchange is seen in some individuals of 

 certain Achatinellidcz. Thus on plate 19, it will be seen that 

 fig. 10 has the normal, tetrataeniate pattern ; fig. 5 is a ' * nega- 

 tive " of it, the black bands occupying the places of the white 

 ones in the other shell. A. crassidentata, pi. 30, fig. 23, is a 

 similar "negative" pattern. In Partulina, P. porcellana has 

 the normal four-banded pattern, while P. nattii has the 

 "negative" pattern. 



The typical group of Achatinella (Apex) never has the 

 four-banded pattern. This is one of the most important dif- 

 ferences between this group on the one hand, and Bulimella 

 and Achatinellastrum on the other. 



Parallel and convergent evolution of patterns. Since 

 many species have forms with primitive streaked pattern and 

 others with distinct bands, it appears that bands have many 

 times been evolved independently. Occasionally this has 

 resulted in the production of strikingly similar varieties as 

 terminal evolution products of several species. Thus, A. vit- 

 tata simulans, A. turgida simulacrum and A. leucorraphe 

 irwini are superficially similar forms, which as their geo- 

 graphic distribution and the less evolved stages of some of 

 them show, have descended from less similar streaked stocks. 



In Achatinellastrum there are some forms of A. ccesia (be- 

 longing to the series of A. livida), which resemble forms of 

 the series of A. vulpina so closely that some authors have 

 actually united them specifically. Yet they inhabit opposite 

 ends of the Main Range of Oahu, and their similarity is 

 merely phenotypic. 



Albino or melanic forms, belonging to different species or 

 races, are sometimes practically identical phenotypically, when 

 the differentiation in shape is slight or variable. 



By the study of many colonies of a species, and of many 

 species, in various stages of evolution, it appears that in all 

 the genera of Achatinellidce the evolution of color-pattern 



