ee —— M — 
volutions ofa some e specimens. 
1. 51A BERN 
Mollusca of Great Britain. 311 
amphibious, since the nature of their food frequently obliges 
them to seek it on wet and marshy ground. During the 
spring they are greatly infested by a minute slender spe- 
cies of Gordius, which in number from two to ten attach 
themselves to the interior of the mantle near its connection 
with the neck of the animal. Draparnaud called them fila- 
mentary organs, and supposed that they performed the office 
of tentacula, probably from seeing them always in motion 
and appearing to issue from the back of the head. ‘This 
troublesome parasite does not seem to be stationary, since 
I have not unfrequently observed it to change its place and 
take up perhaps more commodious quarters in another shell. 
It probably constitutes part of the food of the smaller Dy- 
tiscide. After I had put two sorts (the D. trifidus, and D. cras- 
sicornis, M.) into the glass vessel where the Limnei were 
kept, I could not detect any signs of the Gordii ; though 
in other cases I have known them to survive even after 
their guardians had begun to putrefy. : 
The food of the Limnei is animal and Paaie matter in 
different states of putridity ; which makes them deserve the 
perhaps not inapt epithet of ** Scavengers of the waters." 
In the absence of other nourishment they will even devour 
each other, piercing the shell near its apex, and eating away 
the upper folds of its inhabitant. This accounts for the 
mutilated and often imperfectly repaired state of the upper 
Animal. lubricum, vistidum, sibus, punctis sparsum ci- 
nereis: pallio gelatinoso spiram obtegente. ( Müll.) 
Testa subglobosa, ventricosa, nitida, diaphana, fragilis- 
sima, 
