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THE - CONCHOLOGISTS’ - EXCHANGE 
THE SHELL-BEARING MOLLUSCA 
OF RHODE ISLAND. 
BY HORACE F. CARPENTER. 
Chapter XX XVII. 
186. Planorbis (Gyraulus) parvus, 
Say. 
Synonyms: Helix parvus, Eaton, 1826,; Plan- 
orbis concavus, Anthony. 
Shell small, discoida), color from yellowish 
horn and greenish to black, both sides concave 
and equally exhibiting the volutions ; whorls 
four; aperture rounded; lip rounded and 
sharp, bluish white within. Diameter one- 
fifth of an inch, thickness one-fifteenth. It 
is also found fossilized in the Post-pleiocene of 
the Ottawa Valley. It is quoted as beinz 
found abundantly everywhere, but is seems to | 
be quite local in Rhode Island, the only local- 
ity where it is found abundantly being Cun- 
liff’s Pond, at Elmville, about three miles 
south of Providence. 
Before leaving the genus, I wish to call at- 
tention to a new shell found by me fifteen 
years ago in a small pool near Hammond’s 
pond, in Pawtucket. It is a Planorbis, but 
differs from any species heretofore described 
in any work on American Conchology. Only 
one specimen exists at present. and that one is 
in my collection, and has been examined by 
several conchologists who pronounce it very 
curious and never seen before by them. If 
other specimens are discovered in the future 
and described as new, I wish to announce 
that it was first described by me at a 
meeting of the ‘Providence Franklin Society”’ 
Tuesday evening, February 27, 1871, and the | 
printed description appeared in the “Central 
Falls Visitor,’ the Vriday following. ‘The 
new species. was dedicated to my friend, Mr. 
E. Henry Jenks, of Valley Falls, with whom 
I have had the pleasure of exploring little 
Rhody’s woods and streams for many years. 
187. Planorbis Jenksii, H. F. Car- 
penter. 
Shell small, of a transparent horn color, 
minutely wrinkled by the lines of growth; 
whorls three, separated by a well defined su- 
ture; carinated on both sides and having a 
| miniature resemblence to P. dzcarinatus, spire 
nearly flat; apex sunken a trifle; under side 
forming a broad, shallow umbilicus; aperture 
constricted, the length from top to bottom be- 
ing twice the distance as that from side to side; 
lip thickened and slightly reflected, white 
within. 
This is the smallest Planorbis yet discov- 
ered in the United States. Its size in fractional 
parts of an inch is as follows: Longest diam- 
eter, 8-100; shorter diameter, 7-100; diameter 
of aperture, 4-100 by 2-100. 
GENUS SHGMENTINA. 
Fleming, 1830. 
Synonyms. Segmentaria, Swainson, 1840; 
Discus, Haldeman, 1840. 
The species of Segmentina inhabit Europe, 
Asia and Australia. ‘The two species inhabit- 
ing the United States belong to the sub-genus 
Planorbula, Hald.; they are Segmentina., (Plan- 
orbula), Wheatleyi, a southern species, and 
| 183. Segmentina (Planorbula), ar- 
migera, Say. 
Shell varied in color from light horn to 
regular, slightly concave, showing four vol- 
utions ; under side deeply concave, the whorls 
carinated and bearing several raised revoly- 
ing lines; aperture oblique, inclining to the 
left; lip in light colored specimens dark 
brown or black at the edge (our Rhode Island 
specimens are generally black as coal all over) ; 
within the aperture are five teeth, two on the 
pillar lip, one near the anterior lip, o12e on the 
side of the labium, and two on the upper por- 
tion of the outer lip. Diameter one-fourth of 
an inch, thickness one-tenth. ‘This is a very 
simple and plain-looking shell externally, but 
its remarkable characteristic is the armature of 
black, in some localities nearly white; spire — 
