=Pulmonata.=--The radula of the Testacellidae, or carnivorous land Mollusca, is large, and consists of strong sickle-shaped teeth with very sharp points, arranged in rows with or without a central tooth, in such a way that the largest teeth are often on the outside, and the smallest on the inside of the row (as in _Rhytida_, Fig. 139). The number and size of the teeth vary. In _Testacella_ and _Glandina_, they are numerous, consisting of from 30 to 70 in a row, with about 50 rows, the size throughout being fairly uniform. In _Aerope_ they are exceedingly large, and only eight in a row, the outermost marginal being probably the largest single tooth in the whole of the Mollusca. The central tooth is always obscure, being, when present, simply a weaker form of the weakest lateral; in genera with only a few teeth in a row it is generally absent altogether. [Illustration: FIG. 137.--Portions of the radula of Opisthobranchiata, illustrating types (_b_) and (_c_); =A=, _Scaphander lignarius_ L.; =A´=, one of the teeth seen from the other side, × 40; =B=, _Lamellidoris bilamellata_ L., Torbay, × 60; =C=, _Hydatina physis_ L., E. Indies, × 75.] The first family of jaw-bearing snails, the Selenitidae, is distinctly intermediate. The possession of a jaw relates it to the main body of Helicidae, but the jaw is not strong, while the teeth are still, with the exception of the central, thoroughly Testacellidan. The central tooth is quite rudimentary, but it is something more than a mere weak reproduction of the marginals. There are no true laterals. The Limacidae show a further stage in the transition. Here the central tooth has a definite shape of its own, tricuspid on a broad base, which is more or less repeated in the first laterals; these, as they approach the marginals, gradually change in form, until the outer marginals are again thoroughly Testacellidan.[326] This is the general form of radula, varied more or less in different genera, which occurs in _Nanina_, _Helicarion_, _Limax_, _Parmacella_, and all the sub-genera of _Zonites_. It is certain that some, and probable that all of these genera will, on occasion, eat flesh, although their usual food appears to be vegetable. The jaw is more powerful than in the Selenitidae, but never so large or so strongly ribbed as in _Helix_ proper. [Illustration: FIG. 138.--Portion of the radula of _Glandina truncata_ Gmel. × 40.] [Illustration: FIG. 139.--Portion of the radula of _Rhytida Kraussii_ Pfr., S. Africa. × 25.]