28 



MANUAL OP THE MOLLUSCA. 



sometimes form a single series, overlapping each other, or there 

 are lateral teeth on each side of a median series. The teeth on 

 the pleurae are termed wicini ; they are extremely numerous in 

 the plant-eating gasteropods. (Pig, 15. A.)* 



Fig. 15. Lingual Teeth of Mollusca. 



Sometimes the tongue forms a short semi-cii'cular ridge, 

 contained between the jaws ; at others, it is extremely elongated, 

 and when withdi'awn, its folds extend backwards to the stomach. 

 The lingual ribbon of the limpet is longer than the whole ani- 

 mal; the tongue of the whelk has 100 rows of teeth; and 

 the great slug has 160 rows, with 180 teeth in each row. 



rig. 16. Tongue of the Whelk. \ 

 The front of the tongue is frequently curved, or bent quite 

 over ; it is the part of the instrument in use, and its teeth are 



* Fig. 15. A. Liugual teeth of trochus cinerariiis (after Loven). Only 

 the median tooth, and the (5) Lateral teeth, and (90) U7icini of one side of a 

 single row are represented. B. One row of the lingual teeth of cgproea 

 europcea ; consisting of a median tooth, and three uncini on each side of it. 



t Fig. 16. Lingual ribhon of buccinum undatum (original), from a pre- 

 pai-atiou communicated by \Ym. Thomson, Esq., of King's College. 



