MONOGRAPH OF THE GENUS STROPHIA. 
113 
OBSERVATIONS. 
Variations are chiefly in color. 
No. 1. Pure, snowy white without tinting of any kind, within or 
without. Striations even smaller than in the type and fewer ; a single 
specimen of this beautiful form was obtained. 
No. 2. Flecked slightly with pale reddish, and with more 
numerous and more prominent striations. Shell, thicker and heavier, 
with a thickened margin. 
From this flecked form specimens grade, but through a very 
small percentage, into typical S. curtissii, hence I have not given 
the form full specific rank, as it is an example of an incipient species 
which has not become fully fixed. Known from all other Strophias by 
the short, central tooth and peculiar snowy whiteness. 
DISTRIBUTION AND HABITS. 
I found the Snowy Strophia clinging to the trunk and limbs of 
the banyan tree which stands near the old ruin in the cemetery, where 
Strophia curtissii is found. The back of the banyan is nearly white 
and the shell has assumed a protective color, and, as in most cases 
where a light form of Strophia has become evolved from a dark form, 
the shell has become thinner, thus reducing the size of the striations 
snd margin of the aperture. This lightening of the shell must prove 
beneficial to the animal in living on trees, but in spite of this, we find 
that in order to assist the animal to maintain control over its shell the 
upper tooth has not only beoome more prominent, but the aperture is 
contracted and its margin is extended forward. 
No one can doubt the originator of this form of Strophia, as it is 
now easy to trace it back to its ancestor, and the lesson that it teaches 
us is of great importance in our studies of land shells, more especially 
of this genus. Strophia curtissii is a speeies which lives very near the 
ground, in fact, is frequently found on the ground, hence is liable to 
injury from many causes. Here we find the animal protected by a 
moderately heavy shell, flecked to resemble the mottled bark of trees 
and parti-colored herbage on which it lives. Some offspring of this 
mottled form ascends a white-barked tree, where they are no longer in 
danger of being crushed by the feet of passing animals, but are exposed 
to another class of dangers. Hence gradually through successive 
generations the animal secretes a shell better suited to its new method 
