MONOGRAPH OF THE GENUS STROPHIA. 
123 
jj No. 1, smaller, 1.00 by .50. Whirls, still nine, but with the 
striations much more numerous, 26 to the first whirl. The upper tooth 
is not as prominent, and the color of the shell is paler. 
The Robust Strophia may be distinguished at once in the type 
form from S cinerea by the nine instead often whirls, but there is, as 
stated, some gradations toward the parent stock. 
HABITS AND DISTRIBUTION. 
The Robust Strophia occurs on the north side of Ilog Island 
among some dwarf palms that grow directly back of the beach ridge 
from a sandy soil. They are found clinging to the palm stems or 
leaves. The situation in which they are found is rather sheltered 
and the thickened shell has doubtlessly been evolved as a protection 
against the dryness and heat of the sand among which they live. 
The lack of any extended margin in both this and the parent stock 
would seem to indicate that the animal did not protrude itself as far 
from the shell as is usual in some other allied species. 
The small form, No. 1, occured beneath palm leaves in groups of 
five or six, but neither form were abundant. 
One of my chief reasons for considering this form as a sub-species 
only, is that I found an occasional specimen of typical S. cinerea, 
scattered along a path Avhicli led directly from the beach to Middle 
Bay, on the south side of the island, which is the home of the Cinerous 
Strophia. These shells are doubtlessly transported accidentally by 
persons who pass along the path, and thus as the colony of S. robusta 
receives an occasional recruit from the parent stock, direct inter- 
grades occasionally occur. 
32 STROPHIA CINEREA TRACTA Novo. 
Mottled Strophia. 
Fig. 37, A, front view of type. 
DESCRIPTION. 
Sp. Ch. Size, about medium. Shell, rather thin. Striations 
present. Whirls, ten. Examined, 300. 
Form of shell, a pointed cylinder, the first whirl being the 
largest, then each successive whirl is a little smaller than that above it, 
to the fifth whirl, when the shell slopes to a rather acute point, 
forming an angle of fifty-eight degrees. The striations are rather 
