332 On the Teeth of the Pneumonobranchiate Mollusca. 



lingual membrane is broad ; the teeth numerous, similar, uni- 

 form, in numerous straight cross series on each side of a narrow 

 central equilateral tooth ; the lateral teeth are very nearly equi- 

 lateral, with a broad, flat, subcentral, subeqiiilateral tip. 



OnCHIDIADjE. 



The teeth of a new species of Onchidium, very like O. Cel- 

 ticum, from the coast of West Africa, are very similar to those of 

 Helix, with a short and narrow central tooth in each cross series : 

 the foot of this animal, when preserved in spirits, is quite mar- 

 gined by the mantle and folded across by deep grooves into 

 divisions; the tentacles are completely retractile. 



PeRONIADjE. 



The teeth of Peronia Mauritiana are so like those of Testacellus, 

 that the description and figure of them will almost suit for these 

 (see fig. 1). 



AURICULID^. 



Fig. 3. Auricula. 



The teeth of Auricula (fig. 3) are very like those of Bulimus. 

 The lingual membrane is broad, elongated ; the teeth numerous, 

 in a slightly bent cross series on each side of an equilateral nar- 

 row central tooth; the lateral teeth are rather inequilateral, 

 diminishing in size towards the other edge. 



Lymnead^. 



The teeth of Lymnea, Planorbis, Physa and Ancylus are ex- 

 tremely similar, and have been well described by Dr. Troschel 

 and Mr. Thompson. 



AMPHIBOLIDiE. 

 Fig. 4. Amphibola. 



The teeth of Amphibola nux avellana (fig. 4) are very similar to 

 those of Lymnea. The lingual membrane is large, very broad, 

 expanded and long, with a central space or line scarcely defined ; 

 the teeth are numerous, equal, similar, four-sided, rather longer 



