42 
THE - CONCHOLOGISTS’ 
EXCHANGE 
BRIEF NOTES ON THE LAND AND 
FRESH-WATER SHELLS OF 
MERCER CoO,, ILL. 
BY WILLIAM A. MARSH. 
HERE is, perhaps, no locality in the 
Northern States that can furnish to the 
ardent collector more species of fluvia- 
tile mollusks than Mercer County, Illinois. 
The Mississippi River, which washes its whole 
Western boundary, with its numerous sloughs, 
the great number of small iakes and ponds i in 
the Northwestern part of the County, known 
as the Bog Island, make it a grand repository 
for molluscan life. We have, also, Edwards 
and Pope Creeks running the entire length of 
the County from East to West, and emptying 
their waters into the Misissippi River, besides 
some four or fiv hich 
furnish a few species not found in the river 
proper. An experience of nearly hfteen years 
careful collecting in the waters of this County 
has very likely brought to light about all the 
species that will be found in the County. The 
family Unionide is represented by fifty- seven 
described species, forty-five of which belong 
to the sub-genus C720, five to Alargaritana, 
and seven to the sub-genus Azodonta. 
+ 
Nores ON FLUVIATILE SPECIES, FAMILY 
Unionide, SUB-GENUS Unio. 
1.—Unto anodontoides, Lea. 
This fine and very distinct species (which 
has a geographical distribution from Western 
New York to the Colorado River of Texas), 
is found rather commonly in the Mississippi 
River, and very abundantly in the adjoining 
sloughs. The forms found in the river are 
either of a milky white or light straw-colored 
epidermis; while the forms found in the 
sloughs are beautifully rayed. It is a smooth, 
wide species with a rather thick shell. It 
seems to be quite an active species, for I have 
often found it in considerable numbers very 
near the margin of the river, or slough, in 
times of high water. 
2.—Unio ALsopus, Green. 
This isasparsely nodulous Uzo0, oblique in 
outline. It is found rather commonly in the 
river and usually keeps in deep water. This 
species attains a larve size and when adult has 
a dark brown epidermis. It is very distinc. 
from any other species found in our locality, 
and when once known may be easily identifiedt 
The animal of A‘%so) us is always of a reddish 
or salmon color. 
3.-—Unio alatus, Say. 
This beautitul species occurs rather rarely 
in the Mississippi, but is more common in the 
sloughs along the river. It is a winged or 
symphynote shell and is usually covered with 
dark green rays. The nacre is always of a 
pink or chocolate color. Alatus often attains 
a large size, the finest specimens being obtained 
from the sloughs. 
4 —Unio arctior, Lea. 
This shell is probably only a variety of C7270 
gtbbosus, Barnes. It however differs from g7é- 
doses in having a white nacre and it seems to 
attain a larger size. I have found it in but 
one stream (Edw ards Creek) and regard it as 
a very rare species in this locality. I have re- 
ceived this shell from Ohio, Indiana, Tennes- 
see, Alabama and Arkansas. 
5.—Unio asperrimus, Vea. 
This very fine nodulous shell is very close 
to our Unio lacrymosus, I-ea, differmg in its 
larger size and very much longer and sharper 
tubercles and it is also more inflated. U/zzo0 
asperrimus occurs only in the Mississippi and 
is very rare. I have not found over a dozen 
of this species. 
6.— Unio cafax, Green. 
Capax is one of our finest and most interest- 
ing species. It is found only in the Missis- 
sippi and I regard it as a rather rare shell. It 
is a very active species and when the river is 
low it may be found busily plowing its way 
through the sand. The epidermis is smooth 
and of a yellowish horn color, although occa- 
sionally a specimen may be found having a 
beautiful pink nacre and covered with dull 
