CHAPTER: Ty: 
DIVERGENCE UNDER THE SAME ENVIRONMENT. 
EXPLANATION OF PLATE I. 
Plate I presents 21 species of 8 genera of one family found on five of 
the islands of the Hawaiian group. These islands are within sight of 
each other, having the same climate and much the same vegetation, 
and (with the exception of the different forms of snails) the same spe- 
cies of animal life; and yet how great the diversity presented by the 
species of the same genus, not to mention the greater divergence 
attained by the different genera. These eight genera, and the two 
genera represented in Plates II and III, all belong to the family of 
Achatinellidz, found in no part of the world outside of the Hawaiian 
Islands. These genera, though differing widely in form and habits, 
have one shell-characteristic which does not occur in the same degree 
in snail shells found in other parts of the world. It will be observed 
that the small glassy genus Leptachatina (fig. 5), and the minute Auri- 
culella, with a sharp plate in the aperture (fig. 3), are like the much 
larger shells of the other genera, in that they have a twist in the colu- 
mella. The character appears in a greater or less degree in all the ten 
genera by which the Achatinellide are represented. 
Of these eight genera, Carelia is found only on Kauai, Apex and 
Bulimella only on Oahv, while Amastra (and probably Leplachatina), 
is found on all the isiands of the group, and Auriculella, Laminella, 
and Partulina are found on the central islands, that is, on Oahu, Molo- 
kai, Landi, and Maui. The one arboreal species I have received from 
the island of Hawaii is either a Partulina or a Newcombia, the specific 
name being physa (Newcomb). ‘The typical forms of Newcombia are 
found on Maui and Molokai. Laminella and Partulina find special 
development on Maui, Molokai, and Lanai, where they are represented 
by many species. The genera most characteristic of the island of Oahu 
are Bulimella, Achatinella, and Apex. The most nearly allied species 
from different islands do not completely intergrade as do those from 
the same island. For example, Partulina splendida of Maui (fig. 14) 
does not completely intergrade with P. virigulata of Molokai (fig. 12), 
or with P. varvabilis of Lanai (fig. 13), as it does with certain other spe- 
cies of Partulina found on Maui. ‘The species of this genus have been 
so chosen as to present from each island the form most nearly related 
to Partulina splendida. So also in the case of the Laminella, it is not 
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