MONOGRAPH OF THE GENUS STROPHTA. 
127 
Typical specimens of the Changing Strophia are very beautiful 
and so utterly different from S. cinerea that no one would suspect the 
relationship, but that, too, as stated, complete gradations occur 
between the two. I do not hesitate to affirm, however, that this 
species is of quite recent origin and that it has not had time to 
completely change. My reason for making this statement is mainly 
because I could not find any dead specimens of any forms on the 
ground, as is the case among old established species. This is also true 
in regard to the Mottled Strophia. 
How long it takes to evolve a form of Strophia with characters so 
widely different as those exhibited by this one, it is difficult to say, with 
our present knowledge of the subject. I should think, however, that 
these mollusks, when placed under a widely different environment from 
that under which they had been living, would begin to change in two 
or three generations ; but what the length of the life of a single indi- 
vidual is, and how long it is in coming to maturity is impossible to 
say. Judging, however, from the fact that in the winter it is so 
difficult to find a young Strophia with less than four whirls, that, with 
all my experience, I never saw a specimen with less than this number, 
it is probable that they grow quite rapidly, especially in summer, and 
probably acquire their full size in one year. Twenty years would 
mean much to a colony of Strophia, and would naturally produce many 
changes, while in a hundred years I should think that many species 
would grow old and become extinct. 
Be these matters, which are, after all, somewhat speculative (but 
not, perhaps, as much as they seem) as they may, here we have in 
this Strophia a fine example of the changing of one species into another, 
and also very clearly shows how careful we, of to-day, must be in 
recording all the steps of change in order that future generations may 
benefit by our researches. 
The typical Changing Strophia may be at once recognized by the 
dark color, white, and numerous striations. 
HABITS AMD DISTRIBUTION. 
I found the Changing Strophia on March 29, 1893, clinging to 
shrubs along the rocky, northern shore of the western half of Long 
Key, an island that lies about a mile east of Hog Island. I traced the 
shells westward along the shore as far as the little bay on which the 
Marine Hospital stands and eastward to a sand beach about midway 
