INTRODUCTION. 
9 
Jm 
square yards. A comparatively narrow strip of sand, or naked soil or 
rock, would be sufficient to isolate a colony, and a colony so isolated, 
speedily acquires specific characters. As a rule, a given species occu- 
pies a very limited area, sometimes a few square rods on a small island 
upon which there may be several other species. Generally species do 
not mingle, even if a given species be distributed throughout a section 
occupied by others, each will frequently be found gathered in groups, 
apart from the others. I have, however, found species intermingling. 
Conchologists may take exception to some of my new species, 
thinking, perhaps, that I have used too trivial characters in separating 
them. Believing, however, as I do, that it is the imperative duty of 
naturalists today, to record minute points of differences among animals, 
and when these differences are sufficiently constant to indicate specific 
rank, to emphasize them by giving the group, so signalized, a name, 
I have not hesitated so to designate them, if for no other reason than 
for the benefit of the coming generations. As may be expected, in so 
recently formed species as some of the Strophia appear to be, there is 
much reversion in certain individuals toward ancestral types, produc- 
ing what might at first sight be considered as intergrades, or rather the 
result of a union between two individuals of separate species, but among 
the large number of this genus that I have examined, at least 50,000 
specimens, I have yet to see one which does not present characters that 
refer it to a given species. I have worked the vast amount of material 
that has come into my hands, with the greatest care, and have come to 
the conclusion that there are only two alternatives; either to call all of 
the Strophia one species, or to devide them as I have. Ten years ago, 
I might have thought the former named expedient advisable; now I think 
otherwise, and the species of Strophia given in this monograph, are the 
results of my studies. 
0. J. M. 
Newtonville, Mass., Jan., 1889. 
