112 THE CHICAGO ACADEMY OF SCIENCES. 
one more or less bifurcated, one in the right and two oblique ones 
in the left valve; lateral teeth compressed, lamelliform, the an- 
terior shortest; ligament short; margins plain; muscular im- 
pressions scarcely apparent, submarginal; pallial impression 
simple. 
“Animal: Oval, subglobular; mantle margins plain; siphons 
unequal, not ciliated, short, only united at the base, the bran- 
chial one largest and longest; mouth small, oval, transverse; 
branchie large, unequal, united behind, the inner ones largest; 
foot tongue shaped, triangular, flattened, very extensible.” 
(Tryon. )*+t 
“Posterior part of shell somewhat longer than anterior; 
shell and hinge comparatively stout; beaks rounded without 
caps.” (Sterki, in lit.) 
The cardinal teeth of Spherium (Fig. 10A) are very interest- 
ing, and, generally, quite constant inform. In the right valve 
Fie. 10A. 
Cardinal Teeth of SpH#RIUM STRIATINUM Lam. (x 50). Upper figure, 
right valve; lower figure, left valve. 
there is a single, arched tooth, which is placed so that one end 
of the arch is near the dorsal margin of the hinge plate, and 
the other, somewhat bulb shaped, is near the ventral margin. 
This tooth fits in between two peculiar teeth in the left valve. 
One tooth (the upper) extends from the dorsal margin, in a slight 
curve to the center of the hinge plate. The tooth is narrow and 
elevated. Near the ventral margin is placed the second tooth, 
which is elevated, pyramidal and larger than the upper one. 
The lateral teeth are placed on either side of the cardinal in 
each valve, two teeth (single) being in the left valve and four 
*Structural and Systematic Conchology, Vol. III., p. 186. 
tFor a good account of the anatomy of Sphzrium see Proc, Iowa Acad, of Sci., Vol. 
III., p. 173, 1895, a paper by Mr. Gilman A. Drew. 
