198 THE SCAPHOPODA 
orifice of the shell and subjacent mantle is morphologically the 
anterior or cephalo-pedal aperture. Near the smaller posterior 
aperture the shell, being older, is also thicker. The anterior 
aperture of the mantle has a conspicuously thick border. The 
posterior aperture is emarginated by a ventral sinus and is furnished 
interiorly with a dorsal and a ventral valve, which are capable of 
being applied to one another. ‘The animal lives buried obliquely 
in the sand, only the posterior extremity projecting into the water, 
and therefore it is the posterior aperture that is at once inhalant 
and exhalant and serves for the expulsion of the excrements and 
(Cé(((\\\ 
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Fic. 181. 
Dentaliwm vulgare. A, ventral view of the animal removed from its shell ; B, dorsal view of 
the same; C, right-side view of the same; D, the shell in section; E, right-side view of the 
animal in its shell, with cephalic appendages (captacula) exserted as in life. a, mantle; a, 
longitudinal retractor muscle; @’, fringe surrounding the anterior opening of the mantle- 
chamber ; a’, the posterior appendix of the mantle ; b, anterior circular muscle of the mantle ; 
bo’, posterior circular muscle of the mantle; c, ce’, longitudinal retractor muscle; e, liver; J, 
gonad ; k, buccal mass (seen through the mantle) ; q, left kidney ; s’, anterior extremity of the 
foot ; w, w’, longitudinal blood-sinus of the mantle. (From Lankester, after Lacaze-Duthiers. ) 
the genital products. In the extended state of the animal the foot 
and cephalic tentacular filaments project from the anterior opening. 
The pallial cavity extends continuously from one aperture to 
the other. In the middle and posterior regions of the body the 
liver, the gonads, and even the kidneys, extend into the mantle and 
may increase its thickness to such an extent that the pallial cavity 
is reduced to a rather narrow canal (Siphonopodidae). 
The head is situated at the anterior end of the body on the 
concave or dorsal side. In shape it is a sort of cylindrical 
projection or proboscis, and is contractile but not invaginable. In 
the Dentaliidae its anterior aperture is surrounded by eight palps 
or lobes with scalloped margins, but in the Siphonopodidae it is 
