THE - CONCHOLOGISTS’ - EXCHANGE. 37 
croscopic lines. Shell usually covered with 
faint green rays which disappear with age. 
57.—Anodonta Ferrusactana, Lea, 
Shell smooth, oval and sometimes cylindrical ; 
slightly inflated, sometimes slightly depressed 
posteriorly. The epidermis varies from dark 
olive to light brown. Shell usually covered 
with broad green rays, while specimens are 
found almostrayless. Umbones usually rounded, 
sometimes slightly angular. Growth lines promi- 
nent, often with dark brown concentric lines run- 
ning parallel with them. The beaks are only 
moderately prominent and are covered with 
rather coarse undulations running in a circular 
direction toward the posterior portion of the 
shell. There is one northern species, dodonta 
subcylindracea, Lea, which in some respects may 
be confounded with this shell, but saécylin- 
dracea is a more cylindrical species, has more 
prominent beaks, with finer and more numerous 
undulations than on Ferrusactana. Adult 
specimens of swbcylindracea are more con- 
stricted posteriorly, while those of /v77zsaciana 
maintain their symmetry. This shell is found 
from Ohio to Colorado, through all the North- 
western States. I have just received a speci- 
men from Mr. Charles T. Simpson collected in 
Lodge-pole Creek, Colorado, having a pinkish 
nacre; while Mercer County specimens are 
white, shining, and iridescent. It is found 
here only in Pope and Edwards Creeks and 
has now become very rare owing to the ravages 
of the musk-rats and raccoons. I used to find 
it common in Edwards Creek, associated with 
A. edentula, but have not found a single shell 
of this species for three years. 
To be Continued. 
ON THE DISTRIBUTION OF LAND 
AND FRESH-WATER SHELLS IN 
THE TROPICS. 
BY CHAS. 'T. SIMPSON. 
The fact that many marine species of 
mollusca are widely distributed is a cause of no 
great wonder, since the sea is their home and 
the young are all swimmers, so that by this 
means, and the ocean currents no doubt, many 
specimens appear in localities where we should 
least expect to find them. But the land and 
fresh water mollusks when found in countries 
or islands separated by the sea, are usually ac- 
counted for on the supposition that their sepa- 
rate habitats have been connected by land pas- 
sages since the appearance of existing species, 
or that they were introduced to one or the 
other localities through the agency of man. 
I believe that, in the tropics especially, the 
rivers and the sea may have had much to do 
with the distribution of many of these forms. 
One who has never visited the tropics can 
have no idea of the immensity of the forests of 
that region; or of the wonderful vigor and 
exuberance of vegetable life. In these coun- 
tries where a large annual rain fall occurs, the 
| giant trunks of trees cover the ground thickly, 
forming in many places a solid wall of forest a 
hundred and fifty or two hundred feet high. 
The sun pouring down a flood of brilliant light 
and heat into its depths, literally fills the entire 
space with minor growths of every description; 
lianes and sipos in endless variety, hanging in 
festoons from the limbs above. coiled and 
twisted around each other like writhing serpents, 
or drawn taut like the rigging of a ship, amid 
creepers, water vines, shubbery and broad-leaved 
plants of unnumbered species. These giant 
trunks, often fifteen or twenty feet in diameter, 
are in reality vast aerial gardens bearing aloft 
enormous quantities of Epiphyllums and Phyl- 
locacti, ferns, orchids and air pines, as well as 
the immense growth of vines of every descrip- 
tion. A species of Ficus related to the fig, and 
rubber tree of our hot-houses, often lodges its 
seeds in the forks or on limbs fifty, a hundred, 
or a hundred and fifty feet above the ground. 
This plant, the Matapalo, or Scotch Attorney 
as it is called, sends down a tiny air root which 
reaches the ground and begins to feed the 
plant aboye Another and another quickly 
follow, and then a network of cross-roots are 
formed until the tree is clothed from the ground 
to its loftiest hmbs with fetters that never loose 
their hold until they have strangled its life out 
of it. I shall never forget the feeling of awe 
and even terror that I experienced when, rev- 
erently and with bared head I first stood before 
