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 pleurse are termed uncini ; they are extremely numerous in 

 the plant-eating gasteropods. (Fig. 15. A.)* 



Fig. 15. Lingual Teeth of Mollusca. 



Sometimes the tongue forms a short semi-circular ridge/ 

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

 and when withdrawn, its folds extend backwards to the stomach.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 300 rows of teeth ; and 

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



Fig. 16. Tongue of the 



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. Lingual teeth of trochus cinerarius (after Loven). Only 

 the median tooth, and the (5) lateral teeth, and (90) uncini of one side of a 

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

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



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

 paration communicated by \Vm. Thomson, Esq., of King's College. 



