COLOR PATTERNS. XX111 



has been orthogenetic. Partulina and Achatinellce of many 

 groups have followed the same path, beginning with streaked, 

 leading to banded patterns. While the mutations of any one 

 species may appear to be multifarious, it is clear that progress 

 has been in the direction indicated. It is significant that the 

 early neanic and (in Partulina) the late embryonic stages of 

 banded forms often show the earlier streaked pattern. 



Some forms of Partulina have taken another course, em- 

 phasizing the vertical markings; but in some of these (such 

 as P. helena, P. crassa, Hawaiian Baldwinias etc.), there are 

 forms which are evolving or have reached the banded stage. 



The many-banded stage is the acme of pattern-evolution 

 in AchatinellicUz. So far as we know, it is capable of no 

 further modification except by decadence of pattern. 



We may perhaps infer that the four-band pattern has 

 been inherited from the ancestral stock of Achatinella. It 

 is now present in many species of Achatinellastrum and 

 Bulimella, and in some Mauian Partulinas. Sometimes it is 

 represented by the "negative" or complementary pattern 

 noticed on p. xxii, and very frequently it is imperfect, only 

 part of the bands present, or all wanting. It seems thus to 

 be decadent or in process of disappearing from the modern 

 forms. There seems some ground for the hypothesis that 

 in the present Achatinellid fauna we have evidence of two 

 successive cycles of color-pattern. 



(1) In the earlier cycle there were four dark color bands 

 in definite positions. Of this pattern we see only the final 

 stage, frequently in decadence, or perhaps remaining only as 

 bands on the embryonic whorls. (2) The second cycle is now 

 in the mid-stage of evolution from a streaked or axially striped 

 pattern to one of many bands without definite arrangement. 

 In the ' ' Apex ' ' group and some others, all traces of the four- 

 band pattern has been lost; but in some Achatinellas and 

 Partulinas it lingers on with a later pattern usually super- 

 posed upon it. 



There seems to be no evidence that the axially striped 

 Partulinas and their derivative groups, Perdicella, Newcombia 

 and Baldwinia, ever had the four-banded pattern. 



