4 THE « CONCHOLOGISTS’ : EXCHANGE 
BRIEF NOTES ON THE LAND AND 
FRESH-WATER SHELLS OF 
MERCER CoO., ILL. 
BY WILLIAM A. MARSH. 
(Continued. ) 
4o.—Unio tubcrculates, Barnes. 
This species is found rather sparingly in the 
river and sloughs and very rarely in Pope, Ed- 
wards, and Henderson Creeks. It is very 
constant in its specific characters and is so un- 
like any other shell found here, that when 
once known it cannot be mistaken for any 
other. It is almost always covered with tuber- 
cles. The nacre is usually white, but occasion- 
ally one is found having a salmon colored 
nacre. In Southern waters it is found with 
pink and chocolate interior. It is sometimes 
beautifully rayed. In the river it is generally 
found in the gravel, while in the sloughs it is 
deeply imbedded in the mud or sand. In our 
creeks it is likely to be found in the iron ore 
beds, where it seems to be sluggish in its 
movements and is rarely found in motion. 
41.—Unio trigonus, Lea. 
A solid, heavy, dark brown species, found 
rather abundantly in the river and adjacent | 
sloughs. When young it has beautiful green 
rays and a rather smooth epidermis, and then 
resembles so/zdus somewhat. It varies much 
in its nacre, some being white, others a rose 
color, while others still are pink or salmon. | 
The animal of ¢vzgorus is generally red, but I 
have often found it white. 
finest species and as found here is nearer Mr. 
[.ea’s types than any specimens I have ever 
seen from any other locality. It is a very much 
inflated 
very angular over the umbones, with very 
prominent growth lines. It is an active spe- 
cies and may be found in both deep and shal- 
low water, and does not seem to be critical 
about locality, occupying muddy locations as 
well as sandy or gravelly situations. 
. 
| 
{ 
| 
| 
It is one of our | 
shell with massive, incurved beaks, | 
g2.— Unto lenussimus, Lea. 
This fragile but very interesting species is 
found rather sparingly in the Mississippi. It 
| seems to occur in both shallow and deep water, 
| often burying itself completely in the sand and 
gravel beds. It avoids very muddy bottoms 
; and is never found in the sloughs or lakes. 
_ This species is smooth and wide and is usu- 
ally beautifully rayed. The young specimens 
are crenulated posteriorly which portion of the 
shell is as thin as paper. It need not be con- 
founded with any other shell except U. gra- 
cilis, oblique forms of which sometimes re- 
semble fenzzssinus. 
43-— Unio undxslatus, Barnes. 
This common species is found very abun- 
dantly in all our small streams, but never in 
the river. It has a very wide geographical 
distribution, ranging from Western New York 
to Texas. It isa thick, heavy, solid species — 
| usually covered with from five to seven undu- 
lating folds or plications, and for this very fact 
it is the most common species in our creeks; as 
the coons, musk-rats and hogs cannot as easily 
| break its thick shell as they can the more fragile 
species. Many of our more fragile Unios 
| which were very abundant in our small streams 
| thirty years ago, are now extinct, having been 
| exterminated by the animals before mentioned, 
and the time is not far distant when nothing 
will be left but this robust shell. Ten or 
twelve years ago the collector who was not 
very critical about his specimens, had but to 
find the log where Mr. Coon took his meals on 
fresh-water clams, or the hole where the musk- 
rats went out of the water into the ereek-bank, 
to find many specimens of almost every species 
to be found in the stream. Many collectors 
consider undulatus and plicatus identical, but 
this is not likely to be the case, as I have this 
shell from all the Northern States, from New 
York to Iowa and from the states of Missouri, 
| Tennessee, Alabama, Arkansas and Texas,and 
its seems to maintain its integrity with very 
little variation throughout. I have specimens 
from Ohio and Indiana which approach very 
closely to U. mudtipiicatus but not to plicatus. 
The females of this species are much more in- 
