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THE - CONCHOLOGISTS » EXCHANGE: 
Gemma Toiteni, Stimp. 
Cyrena purpurea, H. C. Lea, 
Gemma gemma, Desh., Chenu., Adams, Dall., 
etc. 
‘Tottenia gemma, Perkins. 
Venus Manhattensis, Prime. 
Shell small, nearly circular, beaks central, 
slightly elevated ; surface shining, covered with 
very minute concentric lines; color white, the 
posterior portion purple inside and out. Length, 
three-twentieths of an inch; height, one-eighth; 
breadth, one-sixteenth. Inner margin crenu- 
lated. inhabits from South Carolina to Lab- 
rador. 
This shell seems to combine the hinge of 
a Venus, the external appearance of a Circe 
and the deep angular mantle bend ofa Dosinia. 
Although the first settlers observed this curious 
little gem and sent home specimens of it to 
England, no one seems to have taken the 
trouble to describe it, until Col. Joseph G. Tot- 
ten, finding it at Newport, R. I., gave a de- 
scription of it in Silliman’s Jour, xxvi, 367, 1834, 
under the name of Venus gemma, Deshayes, 
in 1853, Catal. Brit. Mus., separated the genus 
Gemma from Venus. The same objections to 
this name exist as those given under Venus 
mercenaria. Dr. Perkins, in the ‘‘ Molluscan 
Fauna of New Haven,” proposed the Genus 
Tottenia, which I have used in this work. 
The variety Manhattensis was found near 
Hell Gate, N. Y., by Temple Prime, who de- 
scribed it as a new species in Ann. N. Y. Sye. 
Nat. Hist., vil, 482, 1852. He made it a new 
species on the ground that the interior of the 
shell was white and the exterior straw color, 
and the shape of the shell being more triangu- 
lar, It is extremely abundant in Rhode Island, 
and is found in our bay, from circular to trian- 
gular through all its grades of shape; some 
specimens are pure white; others with the pur- 
ple posterior ; same with the anterior and base 
rose colored and some of a beautiful amethystine 
purple all over, inside and outside, 
FAMILY GLAUCOMYIDA. 
Absent from our fauna (Asiatic), 
( Zo be continued.) 
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BRIEF NOTES ON THE LAND AND 
FRESH-WATER SHELLS OF MER- 
CER CO., ILL. 
BY WILLIAM A. MARSH. 
gi.—Limnaea humilis, Say. 
Shell ovate-conic, thin, translucent. Slight- 
ly wrinkled, whirls from five to six, convex, ter- 
minal whirl very minute, often absent, sutures 
indented, labrum covered with a calcareous de- ° 
posit, umbilicus distinct, color varying from 
reddish brown to yellowish white. ‘This is 
a common species throughout the northern 
tier of States, but rather rare in this coun- 
try. It is found sparingly in small ponds and 
wet, marshy places throughout the whole length 
of our county, especially along Pope and 
Edwards Creeks, also about springs along all 
our inland sloughs. Often found associated 
with Lizmnwa desidiosa and issometimes difficult 
to separate from the species. How long this spe- 
cies may remain buried in the mud, I cannot 
tell, but I have ponds on my land that have 
remained dry for three years at a stretch and 
the fourth year fillmg up with water in which 
the little Zzmn@a humilis were found appar- 
ently as abundant as ever. 
92.— Limnea parva, Lea, 
Shell subturreted, thin, smooth, diaphanous, 
horn color. Subperforated, spire elevated, su- 
tures impressed, whirls five, convex aperture, 
elliptical. This very minute species I find 
about perennial springs, sometimes in water 
troughs, and cattle tanks, very remote trom 
any ponds or sloughs. I have often 
found this little species clinging to the moss 
collected on the sides of my horse trough, 
at my barn well, which is nowhere 
near any pond or slough. How they 
happened to be found here remains 
a mystery to me. I have also found this spe- 
cies in considerable numbers about the margins 
of small basins on my lands that had been dry 
for three or four years. 
93.—Limnea curta, Lea. 
Shell subturreted, thin, shining, diaphanous. 
whirls five to six, terminal whirl very minute, 
body whirl inflated, yellow aperture, small, 
