172 ZOOLOGY. 
\ 
mon snail is an example, is quite peculiar to this group of 
islands, and is characterized by the columella having a spira 
twist, giving it the appearance of being armed with a lamel- 
lated tooth revolving within the shell. The singular fact is that 
most of the genera and all the species are restricted, not only 
to a single island, but to a very small area in the islands. In 
Oahu, an island sixty miles long and fifteen broad, there is the 
extraordinary number of one hundred and eighty-five species of 
Achatinellinz, none of them (with scarcely an exception) found on 
any other of the islands and no species occupying a large proportion 
even of this area. Most of the species are confined to the forests of 
mountain regions; and where, as on Oahu and Maui, there are 
two regions of forests divided by several miles of grass country, 
the island is also divided into two sections, having but few, if any, 
species in common. On the island of Oahu, the two sections 
which occupy separate mountain ranges are divided into many 
minor sections in the following manner. From each side of the 
main range project mountain ranges, which separate deep valleys a 
mile or two in width. Each of these valleys is a subordinate sec- 
tion, having its own varieties, and, in many instances its own spe- 
cies, which are nowhere else. Nearly all the species of one genus, 
found on one mountain range, are connected by varieties presenting 
very minute gradations of form and color. Species of the same 
genus on different islands are not so completely connected by in- 
termediate forms. The family is divided into two natural groups 
of genera. The first group consists of seven genera, — Achat- 
inella, Bulimella, Helicterella, Portulina, Newcombia, Laminella 
and Auriculella; these are all arboreal in their habits, and are 
either sinistral, or both dextral and sinistral. The second group 
consists of three genera,— Amastra, Leptachatina and Carelia; 
these mostly live on the ground, and are dextral. Granting the 
hypothesis of evolution, Mr. Gulick is quite unable to account 
for these singular facts, and many others enumerated in his highly 
interesting paper, on the theory of the Survival of the Fittest, or 
_ any other theory that has yet been brought forward. — A. W. B. 
Hartan’s Hawk anp THE Mexican Cormorant.— Prof. Baird 
=e expressed a desire to see the specimens designated in my 
Catalogue of the Birds of Kansas” as “ Harlan’s Hawk” and the 
u Florida Cerat I sent them to him for examination. Mr. 
