U(j 
monograph of the genus strophia. 
we find a decided tendency to fill in the space between the upper and 
lower teeth. 
When the tooth is not double it is elongated to a great extent^ 
sometimes more than three times its length. With this elongated 
central tooth we also find that the upper tooth is extended forward 
often to the edge of the margin ; a character, which, excepting in the 
extinct species, S. elongata, next described, I have observed in no 
other Strophia. Thus it will be seen that a species of Strophia 
living, as will be seen under the head of Habits it does live, in an 
exposed situation, on a small, wind-swept key, has in order to main- 
tain a better control of its shell, not onlv, in some cases, assumed the 
elongated central tooth, which we find in species which live in 
similar situations, but which in other individuals accomplished the 
same purpose by assuming a double central tooth and has further 
closed the aperture by filling in the space between the central and 
the upper teeth. Again, in other individuais, for the same purpose 
the upper tooth is projected forward. 
Another variation is in color. I have a single specimen of ivory 
white, without and within. This specimen has the double tooth quite 
well indicated, with the space between it and the upper tooth partly 
filled. One or two specimens show faint indications of fleckings 
between the striations. 
HABITS AND DISTRIBUTION. 
On page 13, of the present volume, I have given a diagram of tlic 
singular islet which I have named U Key. I mentioned in the 
article which accompanied this diagram that the eastern and western 
sides, or arms, of the U, wane hilly, and that on the southern portion 
of the key the land was low and sandy. This sandy tract was 
covered with a spare growth of palms and had been the h< me of the 
interesting Ivory Strophia. 
I say “ had been ” for from the western side < f the sandy land, 
which I have indicated by a number of f, to the eastern border of it, 1 
did not find a living specimen of a Strophia, altln ugh the ground w as 
strewui with hundreds of dead specimens in all stages of decay, w ith 
now' and then a perfect individual, but all were bleached perfectly 
white by the sun. On nearing the little hill on the eastern border of 
the sand, I began to find fresher specimens, but not until I came to 
the recks of the hill itself, did I discover a living shell. Then 1 
