216 LIMNJEADJE. 



* Tentacles compressed, triangular, with an auricle 

 at the base ; jaws three, papilliform (fig. 53.) ; 

 the eyes are placed on a small lateral lobe on the 

 side of the base of the triangular truncated ten- 

 tacle ; shell conical, hoodlike, apex subspiral. 

 (Ancylina.) 



3. ANCYLUS. (River Limpet.) 



Animal conical ; body attached to the foot the whole 

 length, and covered with an ovate, conical, 

 Fig. 52. simple shell, which is bent to the 



right, with a central posterior 

 rather obliquely recurved tip; 

 the cavity with a lunate sub- 

 marginal scar, interrupted on the 

 Ancylus fluviatilis. l e ft side, for the passage of the 

 air-tube to the lungs. The aperture of respira- 

 tion and vent are on the left side. (fig. 52.) 



On the tongue of Ancylus there are thirty similar 

 lateral teeth in a straight line on each side of the 

 central tooth ; and then there is a curve through a 

 series of six more teeth, where a trifling change in 

 their form occurs. 



Fig. 53. 



The Jaws of Ancylus fluviatilis 

 magnified. 



a, Upper jaw ; 6, Lateral jaws united ; e, The 

 mouth closed. 



So called from the close connection by which the 

 circumference of the shell is fixed to its attachment ; 

 or perhaps from the conical point, resembling the 



