TS 
50 
CONCHOLOGISTS’ 
> EXCIIANGE 
BRIEF NOTES ON THE LAND AND 
FRESH-WATER SHELLS OF 
MERCER CoO., ILL. 
BY WILLIAM A. MARSH. 
(Continued. ) 
15.—Uhio graniferus, Lea. 
This is a deep-water shell and is rather rare. 
It has been thought by some conchologists to 
be identical with U7 verrucosus, Barnes, but 
such is not the case. It is a thick, heavy spe- 
cies and usually thickly covered with tubercles. 
The nacre is either of a chocolate or copper 
color and very shining. Ihave never found it 
near the margin, but always near the channel 
of the river; being one of those species that re- 
mains very inactive and is found buried deeply 
in the sand and gravel beds. 
16.—Unio gibbosus, Barnes. 
This is a fine species and is nowhere abun- 
dant in this locality. I have never found more 
than a dozen specimens in the river, but it is 
more common in Pope and Edwards creeks. 
It is somewhat variable; the river forms being 
solid and very gibbous in outline, while the 
creek forms are nearly as straight asthe U7. rec- 
¢us, Lamarck, with very much thinner shells 
and narrower teeth. ‘The epidermis is dark 
brown, usually rayed, but very obscurely. 
Nacre either copper or chocolate colored. 
The beaks when perfect are coarsely granu- 
lated. 
17.—Un!0 gracilis, Barnes. 
This is a winged or bialate shell, very thin 
and fragile, but owing to the peculiar texture 
of the epidermis it does not crack badly. It 
is found in the river abundantly and inhabits 
both shallow and deep water, and also occurs, 
although very sparingly, in Pope and Edwards 
creeks. Graci/is is usually finely rayed, but it 
is often found devoid of rays. It is very active 
in its movements and T have often found this 
species with C1. Aeviss?mus in great numbers in 
the river very remote from the channel, crawl- 
ing around in the sand in water but a few 
inches in depth. As far as my observations go 
it Is Our most active species. 
18.— Unio Ihgginsti, \ea. 
A thick and heavy shell with a dark brown 
epidermis; teeth very large; shell oblique in 
outline; nacre white or salmon color. It is 
found only in the river and 1s very rare, as I 
never found more than a dozen specimens. 
Habitat, deep water, near the channel. ‘The 
young are beautifully rayed but the rays be- 
come obsolete with age. It resembles e//ipsis 
somewhat but differs in outline. In its teeth 
and in its high, massive incurved beaks it also 
resembles o7diculatus Hild., somewhat, but 
diifers very materially from that species in its 
outline, teeth and beaks, while it 1s very much 
more inflated. ‘There is a wide difference be- 
tween the sexes of this species 
19.—Unio levissimus, Lea. 
This remarkably fine species is found here 
rather sparingly in the Mississippi River and 
its sloughs and lakes. Like gracif’s it is an 
alated or winged shell and although it closely 
resembles gracz/is in some respects, it is a very 
distinct species, At certain seasons of the 
year it seems to be very active and may then 
be found out on the sandbars where the water 
is very swift and but a few inches in depth. 
The handsomest specimens of this shell are 
found in the river sloughs having a muddy 
bottom, where it seems to be more abundant 
than in the river. 
20.— Unio hgamentinus, Lam. 
‘This species attains a very great sizeand is 
found here only in the river, in deep water and 
is quite common. ‘There are two quite distinet 
varieties, one having a white pearly nacre and 
beautiful green rays when young; while the 
other has a pink nacre with very dark green 
rays and, when young, strongly resembles the 
young of crasstdens. Professor R. E. Call in 
the Bulletin of the Des Moines Academy of 
