LIMNiEADJE. 247 



* * Tentacles compresssed, triangular, ivith an auricle at 

 the base ; shell conical, apex subspiral. (Ancylina.) 



3. Ancylus. (River Limpet.) 



Animal conical ; body attached to the foot the whole 

 length, and covered with an ovate, conical, simple, 

 shell which is bent to the right, with a central 

 posterior, rather obliquely recurved tip ; the cavity 

 with a lunate, submarginal scar, interrupted on the 

 left side, for the passage of the air-tube to the 

 lungs. 



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 

 handle of a cover ; in which case it should be written 

 Ansulus or Ansylus. 



The shell differs from Siphonaria, with which alone 

 it can be confounded, on account of the peculiar form 

 of the muscular scar, and the lateral situation of the 

 apex ; in being thin and pellucid, only finely striated, 

 and covered with a thin olive periostraca. 



It only agrees with Patella'm the outward appearance 

 of the shell, for in that genus the apex is anterior, and 

 in this it is posterior, as in most Univalves. 



This animal has been moved from one family, and 

 even order, to another, as naturalists have settled among 

 themselves, whether it breathed by gills or lungs. 

 Rang places it with the Pleurobranchi, and, observes 

 that it lives on stones and aquatic plants, but that he 

 never observed it to breathe free air. Mr. Guilding 

 (Zool.Journ. iii. 335.) and Treviranius (Journal Phys. 

 183*2, t. 1 7.), who published a detailed dissection of the 

 genus, mistake the valve which closes the opening 



m 4 



