408 Records of the Indian Museum. [VoL. VIT, 
and the small tentacles (t.) occur at the sides of its front edge with 
an eye (e.) on the outer side of the base of each of the two anterior 
ones: the additional tentacle is situated at the base of the fore- 
roof on the right side. The fore-roof may be compared with the 
analogous developments in Bulla, Scaphander, etc., and pl. xxviii, 
fig. 2 shows how it lies over the proboscis If the siphon is con- 
tracted and the anterior edge of the mantle pressed against the 
fore-roof, the proboscis, etc. being contracted underneath and 
pressed up by the expansion of the foot in burrowing, the branchial 
cavity must be fairly effectually closed in front. 
TII.—ALIMENTARY CANAL. (PI. xxx, figs. 5—7). 
The actual entrance to the food canal found on dissection will 
vary a little according to the state of protraction or retraction but 
theze is always a short conjoint section of the canal which then 
divides giving fore-gut above and radular sac below. ‘The cavity 
of the latter is practically nil except just in front. 
There is a cushion for the radula, a membrane with thickening 
on either side, 7.e., one may speak of a pair of cartilages which are 
long and narrow, lath-like in fact. They are bound together by 
the membrane in which they develop and by muscle-fibres joining 
them. ‘There are also muscle-fibres around them and at the sides, 
joining them to the proboscis wall. Some of the fibres run for- 
wards and protract the cushion and others run backwards and 
serve for retraction. The tact that the radula is in an organ (the 
proboscis) which moves back and fore, however, makes the separate 
movement of the radula less important and the odontophore and 
its musculature are therefore less complex than in Gastropods 
without a long retractile proboscis. 
The radula has been described elsewhere. It is reduced to 
one tooth, the median or Rhachis tooth, in each row; the tooth is 
powerful and tridenticulate. The whole radula rests on a strong 
membrane, the front end of which, bent down over the cushion, is 
held by a strong pair of ventral-stretching muscles going back in 
the middle line. 
Muscle-fibres arise also from the sides of the subradular 
membrane and go to join the sheath; they keep the main part of 
the radula tense, pulling it backwards and outwards on either side. 
The glands of importance to the mouth region of the gut have 
their ducts much elongated as they are necessarily massed behind 
the proboscis region. They are:— 
(a) One pair of ordinary acinous buccal glands (R.B.G.). The 
ducts run alongside the fore-gut and get involved in its 
wall, ultimately opening near the junction of gut and 
radular sac. 
(b) One pair of glands (T.B.G.) formed of long, much bent, 
folded tubes. These tubes ultimately unite and the 
united duct curls along in the ventral wall of the radular 
sac to open near the junction of the sac with the fore- 
