GASTEROPODA. 451 



The lingual teeth, like the operculum, have usually a structure charac- 

 teristic of the genera or sub-genera, and are sometimes uniform thoughout a 

 whole family or group of families. They also exhibit minute differences in 

 closely allied mollusks, and promise to be of great value in the discrimina- 

 tion of critical species. Mr. Wilton has ascertained that Patella athletica 

 may be distinguished from the common limpet of our coast by its teeth ; 

 and a similar difference exists between two Cape species, P. apicina and 

 P. longicostata. 



In the account already given of the structure and use of the lingual teeth 

 (p. 27 and 160), it has been pointed out that the Carnivorous families have 

 a retractile proboscis ; and it may now be added that in many instances the 

 aperture of this organ is fm-nished with a prehensile spiny collar (fig. 239 

 and 260), apparently for the purpose of holding the prey whilst the lingual 

 organ is employed in drilling or abrading it. The spinose collar coexists with a 

 lovjer mandible in Boris ; but appears not to be found in the genera provided 

 with an upper jaw. The spiny buccal plates of Natica and Lamellaria are 

 united above, like the lateral jaws of jEoUs, of which they seem to be a modi- 

 fication. The vegetable feeders have a rostrum, or non-retractile muzzle, and 

 frequently a horny u])])er mandible (fig. 260), which is sometimes divided, and 

 forms two lateral jaws, articulated above. The chemical composition of 

 the lingual teeth has not yet been examined by a competent observer. It 

 is not improbable that the opaque brown teeth of Chiton, Patella and Nerita, 

 are chitinous, like the mandibles and pen of the calamary.* 



ORDER I. NUCLEOBRANCHIATA. 



Lingual membrane plane, widening backwards ; teeth 3. 1. 3. (p. l'J9.) 

 Firola, Carinaria, Atlanta. 



Fig. 233. Carinaria cristata, L. (Wilton.) 



* The animal basis of shell is a peculiar organic substance, termed eonchloUne, 

 insoluble in water, alcohol and ether, and resisting the long-continued action of acids ; 

 in caustic alkali it dissolves very slowly; its composition is— H. 5, 9; C. 50, 0; 

 N. 17, 5, and O. 26, 6, (M. E. Fremy, Ann. de Chiraie, 1855, p. 96.) 



