THE GASTROPODA 



in the genera Truncatella, 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- B A 



phora)' there is an incomplete 



internal septum, corresponding 



to the interior margin of the 



aperture, which has become 



Odostomia dipsycha. A, the entire shell, 



seen from the aperture side ; B, the hetero- 



strophic apex, more magnified. (After 

 Watson.) 



Fio. 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) ; 

 p.c, posterior canal of the aperture; s, 

 sutures of the whorls ; w, whorls of the 

 shell ; occupying the axis, and exposed by 

 the section, is seen the "columella" or 

 spiral pillar. The upper whorls of the 

 shells are seen to be divided into separate 

 chambers by the formation of successively 

 formed "septa." (From Lankester, after 

 Owen.) 



/to 



t/n, 



Win, 



Fio. 67. 



Auricula (Alexia) bidentata, removed 

 from its shell, ventral aspect. /, foot ; in, 

 intestine ; k, kidney ; l.p, labial palp ; tn, 

 mouth ; m.gl, pallial gland opening into the 

 pallial cavity; pa, mantle; p.o, pneumo- 

 stome or pulmonary orifice ; te, posterior 

 tentacle ; te', rudimentary anterior tentacle ; 

 vi.m, visceral mass, whose different whorls 

 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 



