ACHATINELLA DIMORPHA. 259 



more squat, the last whorl shorter and more obese. Yet the 

 shapes intergrade, dimorpha colonies sometimes containing 

 shells exactly like some of the longer specimens of curia. The 

 gamut of color-patterns is in part different in the two species. 

 While the distribution of curta and dimorpha does not over- 

 lap, as known at present, there is a long boundary still to be 

 exactly investigated where connecting colonies may confidently 

 be expected. The difficulty of delimiting the curta and 

 dimorpha territories is therefore likely to increase with en- 

 larging knowledge. It may turn out that my attempt to 

 separate curta and dimorpha is impracticable in some colonies. 

 Yet here, as in most tree snails, there has been differentiation 

 between forms of the interior slope and those of the Pacific 

 slope west and north. 



Three mutations have been named as species: dimorpha, 

 yellow, fading to white near the suture, which has a narrow 

 chestnut or blackish band. Zonata, ground-color the same or 

 nearly white, with two blackish bands, at and below the per- 

 iphery, and often a sutural band also. Albescens, base yellow, 

 fading upwards, or whole shell nearly white ; no bands. The 

 zonata and albescens forms ordinarily, perhaps always, live in 

 mixed or hybrid colonies; albescens and dimorpha patterns 

 have also been found together. I do not know that the 

 dimorpha form is found living with both of the others, but 

 it probably is. Mr. Gulick, who obtained these forms when 

 they were abundant, assorted his shells and preserved no 

 indication of their association. 



The areas of distribution of zonata and albescens as given 

 by Gulick coincide exactly. He got both in Waimea, Pupukea, 

 Waialea, Kahuku, Hauula and Kaaawa. Dimorpha was ob- 

 tained in the same places except Hauula; but he got few 

 shells in that valley. While in the following account I use 

 these names for convenience in referring to particular pat- 

 terns, it will be understood that they are not of the nature 

 of subspecies or geographic races, but merely mutations exist- 

 ing in hybrid colonies. While sinistral shells are the rule, 

 there are occasional dextral shells. In Waimea and Pupukea 

 the dextral form is rather abundant. 



