152 
HELIX — ALIMENTARY SYSTEM. 
piilmonates in the aiiterioi- part of the buccal cavity, thong, h the oral 
lobes at the sides ami aliove the mouth, which are furnished with 
ganglia and innervated from the anterior tentacular nerve, have also 
been assumed to be gnstatoiy in function. 
The ^Vllment.iry system in fleliv dxpersn is formed by a muscular 
buccal cavity or pharynx, opening externally by a mouth or oral aper- 
ture, bounded by soft fleshy circular lips, and i)rovided with a hard, 
dark brown, chitiiioiis n])per jaw, strongly convex anteriorly and 
broadly crescentic in shape, with attenuate and rounded ends, and a 
variable number of prominent vertical 
ribs or folds strongly denticulating 
both ujjper and lower 'margins, and 
also sliowing perceptible longitudinal 
striation or lines of increase. There 
is also a i)eciiliar and somewhat pre- 
hensile aj)paratus of an oblong shape, termed the odontophore or 
radnla, which is attached like a tongue to the floor of the mouth, but 
supi)ortcd and elevated in the centre by the gristly odontophoral 
cartilage, and armed with innumerable and characteristically formed 
lecurved denticles arranged iii regularly curved transverse and 
straight longitudinal rows or series, the sjiecinieu figured having a 
transver.se formula of -Ih-l- i;! at its widest part. 
The central tooth is always symmetrically formed with elongate 
basal attachment; the free upper margin is Irroadly reflected with a 
stout median cutting i)oint or mesocoiie and a small lateral ectocone 
Fui. i)ll. — Maiuliltlc or Jaw of an 
llt'ii.v X 8, from Chrislchurch. 
Hams. 
Kk;. 315. — I lalf a transverse row of ilie lin.cual teeth of an atUili ifelix as/>crsa, cullectctl hy Dr. 
h'cliarff near Dublin, showing the modifications in form from the symmetrical centre tooth to the 
(juadricuspate marginals, from a higlily magnified photogruijh by Mr. 'J'. W. '1 liornton. 
Showing the symmetrical median or central tooth, c. ; the first laterals to right and left of the 
median tooth ; the 20ih and 23rd transverse rows iirustrating the transition teeth ; and the 31st, 
3(>lh, list, and 13rd teeth of the marginal series. 
at each side. 'I'he laterals are decidedly a, symmetrical, the inner 
angle (jf basal attachment and the inner cutting 2»oint or endocone 
gradually becoming deficient, but the outer cutting j)oint or ectocone 
is gradually more largely develo2)ed, and eventually, as the marginals 
