8 
GENERIC CHARACTERS. 
GENERAL DISTRIBUTION. 
The species of the genus Strophia appear to be centralized in the 
Bahamas, Cuba and adjacent islands; from these localities they are dis- 
tributed outwardly in several directions, but sparingly and somewhat ir- 
regularly; thus although there are several in Hayti, there are none as far 
as known, in J amaica. They are found on Porto Rico, but there are none 
on the Windward Islands, with the exception of a single species on Cu- 
racoa, south of Guadaloupe. One species only, as far as described, is to 
be found on the continent of North America, S. incana, which occurs 
abundantly at Key West, and possibly on some of the other keys and 
on the mainland. I have reasons for believing, however, that one or 
two other species occur on the Keys and on the extreme southern main- 
land of Florida. In South America, but a single species is known, S. 
antonio from Berbice. Thus it would appear that Strophia is almost ex- 
clusively an insular genus and I have never found them occurring far 
from the sea, even on small islands. 
SPECIFIC CHARACTERS. 
In deciding specific rank I have used the following characters, all of 
which are of vital importance to the life of the animals, one or another 
becoming more prominent under various existing circumstances: Form 
of shell; size; color, external and internal, whether exhibiting general 
tintings or markings; absence or presence of striations, their number 
size and regularity of form; thickness and width of margin; position and 
form of aperture; number of teeth, their size, length and relative position 
in aperture; form and size of animal and of the various internal organs 
when known. 
Before deciding as to what characters could be made available in 
indicating specfic rank, I have have endeavored to thoroughly under- 
stand the range of individual variation, and to accomplish this, I have 
often examined with care, thousands of some species. Individual differ- 
ences vary in number and kind with species, sometimes these are very 
great, often affecting characters that in other species remain unchanged. 
As will be seen, however, under head of Observations, one or more char- 
acters will be found sufficiently constant to render the species in hand 
recognizable. Owing to the results produced by the operations of the 
mysterious laws of evolution, species placed under similar conditions, 
even although occurring in widely divided islands, are similar, yet, al- 
though it will not be impossible for one species to occur in widely separa- 
ted ishmds, I have never seen such a species, as I have always found 
some character possessed by one not found in the other. 
