LAND MOLLUSKS OF OAHU. 243 
Two of these genera, Amastra and Leptachatina, are, for the most 
part, found under the dead leaves of trees in damp places; and one, 
Laminella, is found chiefly on low shrubs, while the remaining five 
* genera are always found on trees or shrubs. Now, it must be remem- 
bered that the climate is tropical, and that the rainfall is so distributed 
through the year that in the shady groves there is nothing to drive the 
arboreal species from their haunts on the leaves or branches of the 
trees. Still further, as this family, unlike most other land mollusks, 
produces its young, not from eggs, but in a living, active form, there is 
no occasion in its life history that requires it to leave the tree in which 
it lives from generation to generation. In the distribution and diver- 
gence of these varieties and species we learn the following lessons: 
(1) Varteties are incipient species, and species are strongly pronounced 
varieties. A full collection of the varieties and species of any poly- 
morphic genus produces an oppressive sense of confusion on the mind 
of anyone who examines it for the first time. This is preeminently 
true of a full collection of the Achatinellide of the island of Oahu. 
Hight genera are represented by a multitude of varieties and species 
which, within the limits of each genus, are, for the most part, com- 
pletely intergraded with each other. As natural selection has not 
removed the intermediate forms, it is impossible to say where a species 
begins and where it ends. Having selected a given form as the type 
of a given arboreal species, we soon find that it inhabits perhaps only 
one or two valleys, say half a mile in width, and only one, two, or 
three milesin length. Beyond these limits it is represented by varie- 
ties that become more divergent as the distance from the home of the 
type increases; and, in the case of the Achatinella and Bulimella, this 
difference is so great that in districts eight or ten miles apart every 
one will admit that the forms all belong to different species. Indeed, 
in many cases, though the same vegetation is present, the habits of 
feeding have changed, while in other cases the form and color have 
changed while the habits remain essentially the same. ; 
Though it is easy to find degrees of divergence which most natu- 
ralists will agree in calling specific, but which in a full collection are 
shown to be completely intergraded, yet if a full collection of the dif- 
ferent forms should be submitted in succession to a hundred different 
naturalists to classify, it would be found that no two would agree as 
to the number of species, and a still greater diversity of opinion would 
be revealed as to where the limits of the different species should 
be placed. This is exactly what we might expect if varieties are 
incipient species, and species are simply strongly developed varieties. 
Such being the case, it is folly to ask that the nomenclature should 
