THE GASTROPODA 83 
in the genera Zruncatella, Cerithidea, Caecum, and Cuvierina, the 
portion of the shell beyond the septum may be truncated and lost, 
or the first whorls may be filled up by a calcareous deposit as in 
Magilus. In the conical shell of various Capulidae (Taenioglossa), 
Zeidvra, and Septaria (Rhipido- 
glossa) and Latia (Basommato- 
phora) there is an incomplete 
internal septum, corresponding 
to the interior margin of the 
aperture, which has become 
" BiG: 65 
Odostomia dipsycha. A, the entire shell, 
seen from the aperture side; B, the hetero- 
strophic apex, more magnified. (After 
Watson.) 
Fig. 66. 
Section of the shell of Triton. a, apex; 
a.¢c, anterior canal (or siphon) of the aperture 
of the shell (a.c to p.c, aperture of the shell) ; Bia. 67. 
p-c, posterior canal of the aperture; s, Auricula (Alexia) bidentata, removed 
sutures of the whorls; w, whorls of the from its shell, ventral aspect. jf, foot; in, 
shell; occupying the axis, and exposed by intestine; k, kidney; /.p, labial palp; m, 
the section, is seen the ‘‘columella” or mouth ; m.gl, pallial gland opening into the 
spiral pillar. The upper whorls of the pallial cavity; pa, mantle; p.o, pneumo- 
shells are seen to be divided into separate stome or pulmonary orifice; fe, posterior 
chambers by the formation of successively tentacle ; te’, rudimentary anterior tentacle ; 
formed “septa.” (From Lankester, after vi.m, visceral mass, whose different whorls 
Owen.) are fused together. 
prominent. In certain genera this septum is folded into the shape 
of a trumpet, the cavity of which affords a lodgment for a pro- 
jection of the posterior part of the foot (Crucibulum, Fig. 69). In 
the last whorl of the shell of Clausilia there is an accessory piece, 
the clausilium, attached to the columellar axis by an elastic 
support: this piece closes the mouth of the shell when the animal 
