114 
THE - CONCHOLOGISTS’ - EXCHANGE. ' 
MARGARITANA HILDRETHIANA (LEA.) 
BY B. SHIMEK, C, E., IOWA CITY, IOWA. 
Many of our species of A/o//usca are consid- 
ered rare simply because, seeking secluded or 
almost inaccessible places, they are seldom 
found by those who are unfamiliar with their 
habits. 
Judging from the notes which have come 
under the writer’s observation, as well as from 
his own experience, Margaritana Hildrethiana 
(Lea) is one of these species. During the 
Summer of 1887 this species was found in such 
numbers, and under such peculiar circum- 
stances, in the Iowa River, Iowa City, that a 
note of it may be of interest. 
Living specimens of this species were first 
discovered after the great overflow of the 
Iowa River, in 1881, when one of our mill 
ponds was drained by a washout. ‘These 
specimens were found burrowing in the mud 
under large stones in such a position that to 
get them it was necessary in most cases to re- 
move the stones. Careful search at different 
times after this brought nearly 200 specimens 
to light, which was considered a very large 
set. 
During the past Summer, however, a search 
on the rocky bottom of the Iowa River, west 
of the city, was rewarded by the discovery of 
several thousand specimans of this species in 
good condition and of all sizes, Nearly all of 
these specimens were found in quiet water bur- 
rowing wder large slabs of limestone in soft 
mud, so that to secure the specimens it was 
necessary to turn the slabs over. Some con- 
ception of their abundance may be found from 
the fact that under a single slab measuring 16 
by 18 inches, three hundred and twenty-four 
specimens were found! It may be remarked 
that the river was very low during the past 
year, and the place was thus made easily ac- 
cessible. No doubt the species exists under 
like conditions in other localities, and this note 
is offered with the hope that it may lead to its 
discovery in like abundance where now it is 
considered rare. 
January 25, 1888. 
NOTES ON AMERICAN SHELLS. 
BY REV. WM. M. BEAUCHAMP. 
The various notes on American shells in the 
COoNCHOLOGISTS’ EXCHANGE, are becoming 
of great value, especially some of those 
on the Unionidze, on which the average col- 
lector finds it more difficult to get reliable in- 
formation than on any other. It would be a 
real boon if the CoNCHOLOGISTS’ EXCHANGE 
could give serviceable descriptions of the spe- 
cies of this great group. Our difficulty is the 
incessant variations in all land and fresh water 
shells in America; a difficulty which I think 
Mr. Ancey hardly appreciates. I have always 
found U. pressus (Lea) a dark green shell with 
rays, but Mr. Benedict, of Syracuse, N. Y., 
has given me some from Jefferson County, N. 
Y., which are orange color and without rays. 
I have U. complanatus (Sol.) so different in 
form, size, and color, that they would certainly 
have been called different species had they 
been found far apart. A radius of five miles 
will not allow oftheir separation. Yet ahighly 
alated specimen from Onondago Lake agrees 
with no description, and a long compressed 
specimen, with beaks nearly terminal, from the 
Erie Canal, seems widely separated from the 
short, swollen valves of some neighboring 
streams. 
Helix albolabris (Say) varies more than 
many suppose. The shell may be thin or 
thick, dentate or not, even in the same locality, 
but the adult specimens that I have collected 
at the Thousand Islands of the St. Lawrence, 
and the Thimble Islands of Long Island Sound, 
are more elevated than, and about half the size 
of, the normal shell. In the same situations 
LH. thyroides (Say) is small. J%elantho decisus 
(Say) varies greatly in adjoining waters, and 
the same thing is true of many shells. 
Some years ago I announced the discovery of 
Bythinia tentaculata (Lin.) at Oswego, N. Y., 
and soon after found it sparingly in the Erie 
Canal at Syracuse. It has now become the 
most abundant shell inthe canal in that vicinity. 
I collected, last Spring, on a gravelly bottom 
in the canal, favorable to Goniobasts Virginica 
and Zivescens, but found only dead shells of 
these, while every stone was occupied by the 
