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THE TEETH OF INVERTEBRATES. 349

of several pieces, more or less overlapping and making the arch flexible,
thus facilitating the protrusion of the buccal mass in feeding. The
Fig. 178.
Fig. 179.

Fig. 181.

Jaws of Pulmonates : Fig. 178. .Taw of Tthonnophorns.—Fig. 179. Jaw of ^riora.— Fiff. 180. Jaw of G/«/)-
tiMlonid.—Fig. isi. Jaw ot Zunites.—Fig. 182. Jaw (A) of Geomalaeus ; B, rachidiau and two lateral
teeth; C, outer laterals.
pieces are united by strong muscular tissue. In many of the marine
forms the arch of the jaw is, as it were, hinged at the keystone by car-
FiG. 183.

j^..,-,aM..,v,^i.,v,o,^;v.u-L^-<-i-|-'i-ivi'i-i-i-!,i*i--- L-!:r.-i=y-'
Fig. 184.
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p) \/%r'^^^'^w? ^^^

Fig. 185.

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Fig. 186.
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Teeth of Pulmonates: Fig. 183. Teeth of A chafhw.—Fig. 184. Teeth of Siphonarin.—Tig. IS.". Teetn
of Siicclnea.— Fig. l-«6. Teeth of Linnxsn ; c, rachidian ; /, lateral teeth. In these figures the teeth
are represented as if seen from above and behind.
tilage, doubtless for the same purpo.se. In the pond-snails (Limncca)
the arch has two small, delicately-hinged lateral pieces, which have a