50 THE - CONCHOLOGISTS’ 
$ 
EXCHANGE. 
here. Some twenty specimens were found 
only, at the junction of the Lakey with the 
Hanneman Slough, near the Mississippi River, 
associated with Pesedtene compressum, and three 
or four specimens were found in Sturgeon Bay, 
above New Boston. 
67.—Pisidium eguilaterale, Prime. 
Shell small, stout, heavy, somewhat inflated, 
rhomboidal, sub-equilateral ; posterior margin a 
little angular; anterior margin rounded; beaks 
central, large, prominent, rounded, not approxi- 
mate; valves solid and moderately convex ; 
strize fine; surface glossy. Epidermis variable, 
yellow, green, or brown. Cardinal teeth small; 
lateral teeth distinct. This species is very rare 
here, and I know of but one locality, a small 
pond near Pope Creek, where but a dozen spe- 
cimens were found, associated with Sphere 
accidentale. 
To be Continued. 
ON THE DISTRIBUTION OF LAND 
AND FRESH-WATER SHELLS IN 
THE TROPICS. — 
BY CHAS. T. SIMPSON. 
(Continued. ) 
But, it may be asked, is it possible that fresh- 
water mollusks may be carried from one place 
to another across the sea on trees? I believe 
they may. 
out and lodged along the rivers and torrents of 
tropical countries; and in the crevices of the 
bark of these trees many species of fresh-water 
shells finda home. Others live among the 
roots of living trees which are washed by the 
water Of streams. In Florida I have collected 
handfuls of Unio fuscatus and other species 
among,the matted roots of trees just under the 
surface of the water. Such trees, washed out 
and carried down stream, would take some of 
their molluscan inhabitants with them. Others, 
carried in floods, with broken, jagged limbs and 
loosened bark, would plow up quantities of 
mud and shells from the bottom and carry 
Great numbers of trees are washed . 
| 
them out to sea, Some such trees might drift 
into bays at the mouths of rivers in other coun- 
tries, and I have seen just such floating in the 
mouths of the Manatee and Caloosahatchee 
Rivers, in Florida. It must be remembered 
that all these rivers, during the rainy season, 
are only very slightly brackish, or even entirely 
fresh, throughout their estuary portions. 
Trees carried into such places, and bearing 
fresh-water shells, might be driven up and 
landed by tide and winds, and a colony of liv- 
ing inhabitants established. Many of the 
shallow bays along the coast of Florida become 
perfectly fresh during the rainy season, as some 
five feet of water falls there in three months, 
and the same thing no doubt occurs in other 
parts of the tropics where the rain-fall is much 
greater. In Florida these bays at such times 
connect with ponds of water on the flat lands, 
so that often for miles the whole country from 
the shore far inland is nearly covered with fresh 
water. 
At the south-western extremity of the State 
are found the Ten Thousand Islands, an in- 
numerable group scattered over a space of a 
hundred and fifty miles of coast separated by 
brackish channels through which the tide flows 
in and out, gradually becoming entirely fresh 
in the region of the Everglades. So there 
would be no trouble about landing a colony of 
fresh water snails on the Florida coast, and the 
only difficulty would be in bringing them across 
could they stand the drying and the salt water 
of the ocean? Everyone who has ever observed 
fresh-water mollusca knows that many species 
will go for a long time without water. Physas, 
Planorbis, Limnzeas, Paludinas as well as some 
of the. Ampullarias, and many others dry up 
in mud at the bottom of ponds and streams, 
and lie dormant until the rains come. In a 
small drain in the woods near Braedentown, 
Fla., I found numbers of Unio hebes buried in 
nearly dry sand, which must have remained 
dormant for nearly nine months of the year, as 
water only ran in it during the rainy season. 
Some of these were taken out, and survived 
for months thrown out in the yard in the full 
sunshine, and without rain. 
Many fresh-water species will live in brackish 
water, as is well known.  Neritina reclivata, 
found in Florida, seems indifferent as to whether 
ne 
