42 



NERITID^. 



phrodite, self-impregnating (?). Shell spiral, or 

 conical, symmetrical. 



With the single exception of Neritina and Proser- 

 pintty all the animals of the sub-order are marine. 



Fam. 1. NEKITID^. 



Muzzle very short, annulated, provided with a hood ; 

 jaws two, one above and the other below, both 

 toothed on the edge. Tentacle contractile, subu- 

 late, pointed. Eyes on short pedicles at the base 

 Fig. 11. 



Neritina fluviatilis. 

 a, foot below ; b, head above ; c, opeixulum inside. 



of the tentacles (fig. 11.^.). Tongue membrane 

 broad, with very numerous series of transparent 

 glass-like teeth; the central teeth (fig. 12.) very 



Fig. 12. 



Teeth of Neritina fluviatilis. 

 a, central. 



unequal; the second and fifth on each side 

 large, broad, dark-coloured; the lateral teeth 



