TEETH OP ACHATINELLIDJE. 399 



whorls with similar longitudinal striae. The conclusion from 

 this and the fact that the young until a late stage have the 

 Achatinelloid form and apertures is 'obviously in favor of 

 the opinion that Apex sprang from Achatinella and not from 

 Bulimella which it resembles more closely in the aperture. 



The close resemblances in the pattern of coloration is in 

 favor of the derivation of Apex through A. plumata or some 

 closely related modification of this polymorphic species. We 

 can now assume as a working hypothesis that Achat. ph&ozona 

 not only lies at the focus of affinities of these genera but was 

 the surviving representative of their common ancestor. If 

 this be the case the young shells, being nearer to the assumed 

 ancestor, Kauaia, ought to carry closer reminiscences of this 

 progenitor and retain its aspect until a later stage of de- 

 velopment than Achat. plumata, Bulimella, or Apex. 



This theoretical requirement is actually more exacting than 

 ought to be demanded in view of the fact that Ach. phaozona 

 is a more or less remote descendant of this ancestor or 

 proachatinellan shell. Like other actual cases of this kind, it 

 might reasonably be expected that it would have lost or 

 skipped in its development many of the characters of this 

 ancestor. Nevertheless, even the most exacting requirements 

 of the working hypothesis are fulfilled in the ontogeny, and 

 not only the form until a late stage of development is similar 

 to that of Kauaia, but the horn-brown and uniform pattern 

 of that genus is also recapitulated in those varieties of Ach.. 

 phaozona that are not banded. 



