THE - CONCHOLOGISTS’ - EXCHANGE. 
103 
Geo. H. Perkins, in the ‘‘ Molluscan Fauna of | BRIEF NOTES ON 
New Haven,” p. 147, 1869, proposed the name 
of Crassivenus for this division. We cannot 
change the specific name, for by so doing we 
deprive Linnzeus of the honor due to him as 
its first discoverer, and at the same time Schu- 
macher is entitled to his generic name by law 
of priority, but for the reason above given and 
to avoid tautology, I think it better to adopt 
Perkins’ genus, although of later date. Con- 
trary to the plan adopted by most Concholi- 
gists, | accept Crassivenus as a sub-genus of 
Venus and reduce Mercenaria to a synonym. 
The variety notata was described by Say, in 
Journ, Acad. Nat. Sci., Phila., 11, 271, 1822, as 
a distinct species. The shell is less solid, and 
does not attain the size of mercenaria; the con- 
centric ridges are not so prominent; the surface 
is not chalky, but shining, approaching a flesh- 
color, and marked with zigzag flashes of a 
darker shade on the lower part of the shell; 
interior of a yellowish white color, without any 
tinge of purple on the margin and several other 
minor points of difference. These points are 
of no value in separating species, as suites of 
specimens can be arranged, showing all the 
grades of variation between the most marked 
opposites ; the colored margin is no criterion, 
as I have young and old specimens having no 
color, and also those with the whole interior 
covered with purple, and others with white 
centres, and the entire margin colored. 
To be Continued. 
NECROLOGY. 
Wm. L. Mactier, Conchologist, at Philadel- 
phia, January 20th, 1888. Mr. Mactier was 
for a number of years an active member of the 
Academy of Natural Sciences, of Philadelphia, | 
and also an earnest student and collector. 
He was Treasurer of the Conchological Sec- 
tion for twenty-one years, in which he was 
succeeded by Mr. S. Raymond Roberts, of 
Germantown, Philadelphia. 
THE LAND AND 
FRESH-WATER SHELLS OF MER- 
CER CO., ILL. 
BY WILLIAM A. MARSH. 
Sub-order Hygrophila. 
FAMILY LIMNA‘ID AE. 
SUB-FAMILY LIMNAIDA. 
Sub-Genus Limnophysa, Fitzinger. 
&7.—Limnea reflexa, Say. 
Shell fragile, very much elongated, narrow, 
brownish yellow, translucent, slightly reflected 
from the middle; volutions six to seven, ob- 
lique, wrinkled transversely; spire acute, termi- 
nal whirls vitreous; body whorl very much di- 
lated; aperture narrow; labrum with a pale 
margin, and dusky red or blackish sub-margin. 
This fine shell is rather common in the North- 
ern States. It is very abundant in all the 
small lakes of our county, and is also found in 
some of the larger ponds, in the Mississippi 
River bottom, but is found nowhere else except 
in times of very high water, when these shells 
are carried out of the lakes and then may be 
found in considerable numbers along the river 
clinging to limbs of trees and pieces of bark. 
Swan lake, on the Bay Island, is the place 
where this fine shell may be found most abun- 
dant. From the middle of May to the middle of 
June is the time to look for this shell. During 
this period it seems to be ,in the heighth of its 
glory, At this time vast numbers of them may 
be seen feeding on the various kinds of water 
plants, floating, shell downwards, on the sur- 
face of the water. From the middle of June 
they begin to disappear, burying themselves in 
the mud. 
58.—Limnea desidiosa, Say. 
Shell oblong, sub-conical, whirls five, very 
convex, the fourth and fifth very small, the 
second rather large; suture deeply indented, 
aperture equal to or rather longer than the 
spire; labrum, caicareous deposit copious, not 
perfectly oppressed at base, but leaving a very 
small umbilical aperture. This is our most 
