RADULA OF TULMONATA 



231 



Pulmonata. — The radula of the Testacellidue, or carnivorous 

 land JMolhisca, is large, and consists of strong sickle-shaped teeth 

 with verj' 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 

 Ehytida, 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 through- 

 out l)eing fiiirly uniform. In Aero2)c they are exceedingly large, 



Fig. 137. — Portioiusof tlierartula 

 of Opisthobranchiata, illus- 

 trating types {b) and (c) ; A, 

 Scaphander li(/narius L. ; A', 

 one of the teeth seen from 

 the other side, x 40 ; B, 

 La^neUidoris hilamellata L., 

 Torbay, x 60 ; C, llydatina 

 j)hysis L. , E. Indies, x 75. 



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. 



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 



