LIMN^US. 199 



* Tentacles short, compressed, triangular, loithout any 

 auricle at the base; jaws 3, smooth (fig. 47.); 

 shell oblong, spiral. (Llmnosana.) 



1. LiMN^us. (Mud Shell.) 

 Animal with a short broad foot, broad short com- 

 pressed tentacles, without any auricles at the 

 base, a large upper and two small rudimentary 

 lateral jaws (fig. 47.), a large central spiral body, 



^ig- ^'^' The jaws of Limnaus auricularius 



^-5L^ magnified. 



<illillliJ»'> TT • 7 -D V . 1.1- 



^ a. Upper jaw; b. Kudimentaiy lateral jaws. 



and a simple-edged mantle, covered by an ex- 

 ternal ovate, thin, dextral, transparent spiral 

 shell with an ovate mouth, having a single ob- 

 lique plait on the middle of the column run- 

 ning into the axis (fig. 48.). 

 LimncBus has a small central tooth, as it were 

 squeezed up between two very large lateral ones, 

 each primary lateral having a very large apex in- 

 ternally, with a small external one, while at the 

 edge they have altered to one thick prolonged 

 apex projecting inwards and irregularly lobed on 

 its upper edge. 



This genus is known from Amphipeplea and Physa 

 by the edge of the mantle not being produced so as 

 to cover the shell, and by the inner lip not being 

 extended over the body whorl of the shell. It is 

 known from Aplexus by the shell being dextral, and 

 having the pillar-plait ; the latter character, and their 

 greater solidity, will distinguish even the reversed 

 monstrosities of these shells from that genus. 



O 4 



