496 Gross Anatomy of Campeloma. 
C. coarctatum Lea and C. exilis Anthony. The same unfortunate 
cause of synonomy has led, in the genus Unio, to the erection of 
more than a hundred spurious species, in certain cases the females 
serving as a basis for not less than five specific names. The form 
of a shell in so extremely variable a group is certainly a very mis- 
leading character. 
Digestive Organs.—The buccal cavity opens on the middle side 
of the rather short proboscis near its base. Near the cesophagus 
(III., Fig. 3) and upon the floor of the buccal mass lies the radula. 
This is a small, narrow, chitinous organ, beset with numerous trans- 
verse rows of teeth, arranged according to the formula 3.1.3 (Fig. 
3, Plate VII., and Fig. 4). The dentition is therefore teenioglossate. 
On either side, near the posterior end of the buccal cavity, open 
the ducts of the salivary glands (II., Fig. 3). These are small 
racemose paired glands, dirty white in color, and lie close upon the 
cesophagus. Including their ducts, they are about 1.5 mm. in 
length, and nearly or quite .25 mm. in width. The csophagus is 
long, irregularly winding, placed upon the floor of the branchial 
cavity, and opens, into a somewhat capacious stomach (IV., Fig. 3), 
near the middle of the whorl next the body-whorl. The intestine 
is of nearly the same size as the cesophagus, and does not enlarge 
until the opening of the biliary duct is passed (V. and VII., 
Fig. 3). At this point it is coiled upon itself to the left, forming 
what may be called the right duodenal fold, immediately under 
which lies the testis, as stated above. Turning again to the right, 
it is there directed forward, becomes slightly enlarged, forming the 
rectal portion of the intestinal canal (WIII., Fig. 3), which opens 
into the branchial cavity near the margin of the mantle on the right 
side (IX., Fig. 3). The liver (VI., Fig. 3) is a very large gland- 
ular body, completely filling the first two and a half to three whorls 
of the shell, Its contents are discharged into the duodenal portion 
of the intestine near the position of the heart. In color it is orange- 
red, and is somewhat larger and darker in the male than in the 
female form. This organ, like all other portions of the animal 
which lie next the shell, is inversed by a thin membrane, contain- 
ing pigmentary matter, the membrane itself being a continuation 
of the mantle. 
Respiratory Apparatus.—The branchial cavity is large, extend- 
ing backwards throughout nearly the whole length of the body- 
whorl. It opens towards the right side, its left margin being just 
