72 
MONOGRAPH OF THE GENUS STROPHIA. 
and the outer posterior portion is slightly produced backward, but there 
is no prominent edge. The frontal bar is well developed and the stria- 
tions do not appear within it. 
Color of shell, externally, white; internally, pale purplish brown 
which gradually fades into yellowish white on the teeth and walls with- 
in the aperture. 
DIMENSIONS. 
Size of type, .90 by .40. Largest specimen, 1.00 by .43; smallest, 
.78 by .34. Greatest diameter, .43; smallest, .34. Longest specimen, 
1.07; shortest, .85. 
OBSERVATIONS. 
While a large percentage of the specimens of this species clesely 
resemble the type, there is a tendency to assume a more pointed form 
with a less number of ridges, thus bearing a somewhat close resem- 
blance to S. acuta, but I have never seen a S. perplexa that could not 
be separated from that species by the presence of more or less ridges, 
and by the greater thickness of the shell and its whiter color. On the 
other hand, some specimens exhibit an inclination to assume striations, 
irregular and widely separated, thus approaching S. intermedia, but 
the striations are never decided enough for intermedia. In possessing 
these characters, however, the Ridged Strophia is between the Pointed 
and Intermediate Strophias, and at first occasioned me considerable per- 
plexity, as it appeared to form a connecting link between the two. But 
as S. perplexa occurs on Cayman Brae, apart from other Strophias, and 
is thus widely separated from either of the tvro closely allied shells, and 
like many species having apparently obscure characters, taken individ- 
ually, yet while in mass, show strong differences, I soon saw that I 
could not consistently do otherwise than to consider it a distinct species, 
as above described. 
Knowm from all other species, by the absence of striations but 
presence of ridges, white color, and heavy shell. 
DISTRIBUTION AND HABITS. 
The Ridged Strophias occur on the island of Cayman Brae in a 
barren, rocky section, about two miles from the w T est end of the key, 
and a quarter of a mile from the south shore. They were restricted 
to a very limited area, and I found them clinging to low herbage or to 
the naked rock, in almost every instance, exposed to the burning rays 
of a tropical sun. 
