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348 DENTAL ANATOMY.

odontophore as in the T(eniofjlossa. In this group most of the species
have a well-developed mandible or jaw, usually hinged in the middle
line with a softer cartilaginous portion.
Fig. 174

Ehiphidoglossate Teeth : Teeth of Haliotls.
The last of the great groups among the dioecious mollusks is that of
the Docofjlossa (plate- or chevron-toothed), which includes the limpets,
and is divided into three principal subdivisions—one [Acmcea, etc.)
without a rachidian tooth, and rarely with uncini ; another (Patella,
etc.), with well-developed uncini and laterals, and generally no rachid-
FlG. 1

Fin. 175.
Fig. 176.

Docoglossate Teeth: Fig. ITo.—Teeth of Leneta fvlra.—Yig. 116. Teeth of Acmasa virginea.—Fig. 177.
Teeth of Patella vulgala.
ian ; the third (Lepcta), Avith a large rhachidian, without laterals, but
having uncini. All these forms have a well-developed jaw, and all are
marine. They are very archaic in their characters.
It merely remains to indicate the types of dentition among the her-
maphrodite mollusks, the majority of which are air-breathers, but which
have also many marine representatives, and a few which, like Limncca,
the conmion pond-snail, breathe air, but live in the water, or, like
Siphonaria, live by the borders of the sea, and are prepared with gill
and lung to breathe Avhatever comes handiest.
The Helices (which are found under rotten logs, etc. in almost any
woodeo place, and are recognizable by their depressed sjiiral shell and slug-
like body) have a tyjiically pavement-like dentition. This resemblance is
common to many allied groups, such ii'ri AcJiafina, SipJwnaria, Succinea,
etc., and the pond-snails, Lhmum, Planorbis, and others. The most
interesting and little known are the Phj/sas, a group of beautifully pol-
ished pond-snails with a sinistrally wound shell.
The annexed figures indicate the character of the jaw and teeth in
several of the air-breathing mollusks. In some others the jaw is formed