394 HYATT: GENEALOGY OP ACHATINELLIDvE. 



from Oahu, as the first locality in which the group origin- 

 ated. Partulinella dubia of Oahu is probably a remnant 

 of an ancient series which probably sprang from large 

 Amastras having no tooth-folds and also possessing the zig- 

 zag or barred reticulated pattern not very widely different 

 from that of Am. transversalis. 



The Sub-series of Partulinella tappaniana: These are 

 shells with white or light backgrounds and slightly banded 

 patterns resembling mighelsiana and those of the variabilis 

 series that are albinos, but in these every species has through- 

 out, or in some individuals, a pattern barred or marbled with 

 brown in the young. 



Partulinella dwightii of Molokai and lignaria of West 

 Maui belong to both sub-series. The former connects with 

 P. crassa of Lanai. Some of its varieties are marbled through- 

 out life, and some are white except for the zigzag bars in the 

 earliest neanic sub-stage. 



Some of the shells of Partulinella proxima of Molokai are 

 very close to this series as are also P. tappaniana Ad., at- 

 tenuata Pfr., terebra Newc., ampulla Gul. of West Maui, and 

 P. eburnea Gul., P. dolei Bald., and P. nivea Bald., of East 

 Maui. The difficulty in distinguishing highly retrogressive 

 shells of this sub-series from those of the variabilis series is 

 perhaps at present insuperable. Some of the P. tappaniana 

 series such as dolei and eburnea may belong to this sub-series. 

 That is to say, their completely albinized young may have 

 originated in the same way as the completely albinized young 

 of most shells in P. tappaniana Ad., for example, through the 

 non-appearance of the barred pattern in the individual. 



Relationship between Perdicella and Partulinella: Sykes, 

 Fauna Hawaiensis, p. 329, has selected A. helena Newc., as 

 the type of Perdicella Pease, and I propose to follow him. 



Perdicella helena of Molokai is one of the stoutest of the 

 dwarf forms composing this group. Its colors and patterns, 

 basal band and toothless columella, barred young, and finely 

 wrinkled surface due to the crossing of the transverse ridges 

 of growth by longitudinal ridges, show that it is a dwarfed 

 form derived from some species of the Partulinella marmorata 



