398 HYATT: GENEALOGY OF ACHATINELLID^E. 



neani-c stages. This common ancestor probably was not dis- 

 tinct from [Cyclamastra] generically, but must have differed 

 in having a slightly less depressed or longer spire and smaller 

 umbilical perforation, and no distinct carination, the sides 

 being, however, distinctly angulated. 



The young shells of these genera have a common form 

 which may in general terms be described as the nepionic or 

 baby shell. This has a comparatively smooth short spire with 

 open columella and broad, stout volutions showing a tendency 

 to angularity on the outer, median zone of the volution and 

 some times an incipient carination. This is particularly ob- 

 vous in species of Amastra, and in Achatinella ph&ozona and 

 Ach. plumata, which are both closely allied species. 



There is but one form among Achatinellida that is geneti- 

 cally identical with Ach. phczozona and A. plumata. This 

 is Kauaia, a terrestrial genus of the island of Kauai. This 

 shell has until a very late, probably adult stage, a similar 

 stout form and visible carinations, and its brown color is also 

 in accord with the similar hues of many young shells. The 

 terrestrial genus Amastra is obviously in the direct line of 

 descent from Kauaia, and has similar colorations and uniform 

 pattern. 



Achatinella phceozona, now extinct, was collected by Gulick 

 in the valley of Kuliouou immediately adjoining Niu. This 

 species shows characteristics that intergrade on the one hand 

 with Bulimella and on the other with Achatinella. It stands 

 at the focus of the affinities of these two groups as regards 

 the form of the shell, which is bulimelloid in some varieties, 

 and Achatinelloid in others; and in the apertures which are 

 plainly Achatinelloid. It also grades into A. plumata 

 through numerous hybrids. 



Apex cestus and forbesianus are both in color and in pat- 

 tern more like Achat. plumata than any other species of the 

 same region, but differ in the characteristic, turbiniform 

 basal volution, the Bulimella-like aperture and the almost 

 constantly dark apex of Achat. plumata. Achat. plumata 

 has also the dark apex and is precisely similar to Ach. por- 

 cellana, which is almost white in the succeeding or nepionic 



