THE - CONCHOLOGISTS! -{EXCHANGE: 
49 
S. ¢runcatum and S. partumium. It differs 
from the former in being more inflated, more 
angular, less round, beaks less central; and 
from the latter in being more equilateral, much 
more abrupt on the anterior and posterior mar- 
gins, more rounded at the base It is much 
larger, more elongated, and with a lighter col- 
ored epidermis. I find it usually associated 
with strzatinum and transversum. 
62.—Spherium trancatum, Linsley. 
Shell rhombic orbicular, lenticular, thin pel- 
lucid, slightly inflated, nearly equilateral, an- 
terior margin rounded, posterior margin straight, 
beaks central, calyculate, and approximate at 
the apex, striz very delicate. Epidermis light 
green to dark brown. Cardinal teeth small, 
lateral teeth slender. 
I have neyer found this species in the vicinity 
of the river, but it. formerly occurred quite 
abundantly in all the small ponds along Pope 
‘and Edwards Creeks. Three years ago, in 
the month of November, I collected over 2000 
specimens of this shell in one small pond near 
Pope Creek, that had quite recently been 
drained, and the water all drawn off. This 
appears to be a very sluggish species, moving 
around but little, although it seems to like 
muddy situations. I never found it buried in 
the mud, nor have I ever seen the animal in 
motion. 
63.—Spherium occidentale, Prime. 
Shell oval. small, pellucid, fragile, equilat- 
eral; margins rounded; valves slight, sometimes 
convex, at times rather depressed; beaks full, 
rounded and raised slightly, sulcations very 
fine. Epidermis varying from yellowish to 
brownish horn color. Cardinal teeth small; 
lateral teeth larger. This species is probably 
very rare here. Five years ago I found about 
20 species ina small pool of still water near 
Pope Creek, in Cabeen’s timber, which is the 
only locality known to me. 
64.—Spherium transversum, Say. 
Shell oblong, elongated, inequilateral, trans- 
lucent, anterior margin rounded, posterior mar- 
gin truncate; beaks prominent, calyculate; 
striae very fine. Epidermis greenish yellow, 
often of a darker shade over the beaks. Cardi- 
nal teeth compressed; lateral teeth long. 
This large and well-known species is com- 
monly found in the river and in its lakes and 
sloughs; and it is also found in Edwards 
Creek. The young specimens are very fragile. 
The species has a geographical range from 
New York to Texas. 
GENUS PISIDIUM, PFEIFFER 
Animal elongate oval, compressed laterally ; 
lobes of the mantle without tentacles, united 
posteriorly into a single, short syphonal tube ; 
tentacles of the mouth triangular, elongated ; 
gills of moderate size; foot small. The differ- 
ence in the sfed// of Pisidium, and that of Sphe- 
vium, consists mainly in the position of the 
beaks, which, in P%s¢dzz, are terminal, and 
in Spherium, generally central, dividing the 
hinge margin into equal portions. 
65.—LPisidium conpressun, Prime. 
Shell solid, oblique, trigonal, triangular, in- 
flated; beaks small, but raised and distant, with 
a wing-shaped appendage on the summits; 
striz distinct and regular. Epidermis variable, 
yellow-brown, sometimes chestnut color. Car- 
dinal teeth small; lateral teeth short. 
This is our most common species, and is 
found very abundantly in the sloughs, and in 
the small lakes of the Bay Island. . The finest 
specimens are found in Sturgeon Bay, above 
New Boston, and in Swan Lake. During 
the Spring this species is very active, but in the 
Autumn it is seldom found. Owing to the pe- 
culiar wing appendages on its beaks, there is 
no difficulty in separating it from other species 
of this genus. 
66.—Pisidium variabile, Prime. 
Shell heavy, oblique, inequilateral, inflated, 
subtruncate; beaks situated posteriorly, full, 
prominent, not approximate at apex ; #valves 
solid; strize regular and distinct. | Epidermis 
varying from straw color to greenish brown, 
darker anteriorly than posteriorly. Cardinal 
teeth united, small; lateral teeth short and 
heavy. ‘This species is by no means common 
