6 THE CHICAGO ACADEMY OF SCIENCES. 
rate, the lateral margins being pointed. The tentacles are large, tri- 
angular and placed on top of the head just above the junction of the 
vela area with the foot. The black eyes are placed on small swellings 
at the inner base of the tentacles. The mantle fits closely to the aper- 
ture of the shell, but does not extend beyond the margin of the outer 
lip or the edge of the reflected inner lip. The respiratory orifice is placed 
near the posterior angle of the shell, where a portion of the mantle 
is modified to form a so-called siphon which is capable of great ex- 
pansion when the animal is taking in air. The pulmonary cavity fills 
about half of the body whorl and is usually colorless and transparent 
as seen through the shell. The heart may be distinctly seen through 
the thin tissues and its pulsations easily counted. 
The heart pulsations of several specimens are tabulated below: 
LENMNEU SIACNAIS are race ee 37- 48 per minute. 
Pseudosuccinea columelia.............--.-- 53- 60 “ o 
GOLOGUODTUSSA ete ne See ee ee OG 150-155 HE 
Galba humilis modicella....5.0....0.2005--% 140-146 “ y 
GOLDARCOP COLO sata ee ee tee 1129-133 “ ss 
GOOG POLW SUAS aos oak ae cee 8 ee Rite ete 80- 81 “ S 
The smaller species appear to have a higher pulse than the larger 
ones, stagnalis, the largest species, having 37-48 pulsations, while 
obrussa, one of the smaller species, has 150-155 pulsations per minute. 
There are no grooves on the body as in the helices, and the texture 
is smooth instead of being granular. The shell is carried, as a rule, 
in a direction parallel with the foot, although it may at times be swung 
around until it rests obliquely or even at right angles to the foot. (Fig. 
H.) In color the animals vary from yellowish, flecked with whitish 
or yellowish spots, to jet black. Frequently the black dashes, spots 
or blotches of the mantle may be seen through the transparent shell, 
causing the latter to appear mottled. The foot and tentacles vary to 
some extent among the different species, the variation being in the 
length of these organs. 
3. GENERAL INTERNAL ANATOMY.; 
If a large specimen of Lymnza be opened on the back and the 
organs be carefully separated and spread out (as in plate 1), the 
relations and characteristics of the various anatomical features may 
be easily made out. In the plate, the genitalia are turned to the left, 
while the digestive and respiratory systems are turned to the right. 
1This topic is treated in a somewhat superfiicial manner, the purpose being 
simply to point out the more obvious characteristics of the various organs. 
The common American Lymnaeid, Galba reflexa Say, has been selected for this 
purpose. 
