LIMN^US. 
199 
* Tentacles shorty compressed^ triangular^ without any 
auricle at the base; jaws 3, smooth (fig. 47.); 
shell oblong^ spiral. (Limnceana.) 
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. 
Fig. 47. 
a- 
The jaws of Limnceus auricularius 
magnified. 
a. Upper jaw; b. Rudimentary 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.). 
Limnceus 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. 
