62 THE - CONCHOLOGISTS’ 
- EXCHANGE 
BRIEF NOTES ON THE LAND AND 
FRESH-WATER SHELLS OF 
MERCER CoO., ILL. 
BY WILLIAM A. MARSH. 
(Continued. ) 
25.—Unio multiplicatus, Lea. 
A very rare plicate species found in the 
sloughs of the Mississippi River and in the lakes 
of the Bog Island. No more than a dozen speci- 
mens of this shell have been found within the 
boundary lines of this county to my knowledge. 
Those found here seem to be more inflated than 
those collected in Tennessee and Ohio streams. 
The species attains a large size. 
26.—Unio Mississippiensis, Conrad. 
A rare shell of the Masutus group.  Sup- 
posed to be identical with (220 swbrostratus, 
Say, but a much larger shell. It is a rare 
species, found in the sloughs of the Mississippi 
River. I have never found it in the river. 
seems to avoid running water, being found 
where the mud is quite deep. 
27.—Unto occidens, Vea. 
This is the female of Unio subovatus, Lea, 
and belongs to a natural group of some of the 
finest of our American species including szd- 
ovatus, ovatus, capax, ventricosus, ochraceus, 
Canadensis, excavatus, lineatus, satur, perdix, 
dolabreformis, cartosus, etc. Its nearest con- 
gener here is vestrvicosus, Barnes. 
our small 
ago, quite abundant, but is now rarely found. 
Occidens is a very inflated shell having few 
rays, many specimens being devoid of them - 
altogether. The nacre is white, sometimes 
It | 
It inhabits | 
streams only, where it was, years cially when young),the folds are very obscure. 
pearly; the teeth are large and the shell some- | 
limes attains an immense size. It seems to 
delight in muddy bottoms. The time is not 
far distant when this shell will be entirely 
extinct here, as will be the case with all our 
Uniones which make the creeks their sole hab- 
itation. 
28,.— Unio pustulosus, Lea. 
This, as the name implies, 
species; subrotund in outline, and may be 
distinguished from other 
group by its greenish color over the umbones. 
It is found only in the river and is a ceep- 
water species, being found usually half buried 
in the beds of sand and gravel. It is some- 
times thickly covered with pustules, while other 
specimens are nearly smooth. The nacre is 
usually white and pearly, but I have found a 
few having a slight pinkish tinge. It is very 
abundant here. 
29.— Unio pustulatus, Lea. 
A very fine pustulate species, with a dark 
is a pustulose — 
members of this | 
brown or chestnut colored epidermis, easily — 
separated from pzstulosus by its fewer and 
larger nodules and its dark, concentric lines of — 
It is a river shell with habits very © 
growth. 
similar to pustudosus. 1 find that it is very rare 
here, having found not more than a dozen 
specimens during the many years of my col- 
lecting. 
j30.— Unio plicatus, Leseuer. 
This plicate shell is found abundantly in the 
river, its sloughs and in the lakes of the Bog 
Island, preferring muddy bottoms, where it 
attains an immense size. I[t has a dark brown 
epidermis, but is quite variable in its interior. 
Some have a chalky white nacre; some are 
shining and iridescent, others have a dull, sal- 
mon-colored nacre, while many are tinged 
with purple all around the margin of the shell. 
The young of this species are very globose and 
much inflated. On some specimens (espe- 
37.— Unto parvus, Barnes. 
This little species is found quite commonly 
in every portion of our county where there is 
water having a muddy bottom. It has a very 
dark brown epidermis, rough and striate with 
| beautiful undulations on its beaks, and a bluish 
white nacre. Atcertain seasons it is very active, 
and és the first species to claim the attention of 
the collector in early spring. 
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