This fine insect, the largest of our water-beetles, has remark- 
ably strong and curiously denticulated mandibles (not unlike 
the under jaw of some Mammalia): its entire labrum, short 
2nd joint of the antennae, bifid claws (not recurved at the 
base), and the attenuated elytra, are also very different from 
those of Hydrophilus caraboides , to which it is most nearly re- 
lated ; and the singular structure of the male anterior feet is 
confined to our insect. 
The larva of Hydrous is a soft disgusting animal, living ap- 
parently amongst the mud in ditches : it is full-grown in July, 
when it leaves the water and forms a cell under dung or in 
the earth, where it becomes a pupa. The female beetles of 
this family, like spiders, deposit their eggs in a web. “ In 
form,” says Mr. Kirby, speaking of the egg-pouch of II. pi- 
ceus , 66 it somewhat resembles a turnip when reversed, the 
greater diameter of which is f ths of an inch.” “ At its base is 
the opening prepared for the egress of the larvae when hatched, 
which is closed by some threads, that, by means of the air con- 
fined in the cocoon or pouch, hinder the water from getting 
in. This nidus does not float at liberty in the water till after 
the eggs are hatched, the parent animal always attaching it to 
some plant. By means of this anomalous process for a beetle, 
which this insect is instructed by Providence thus to perfect, 
the precious contents of its little ark are secured from the ac- 
tion of the elements which is to be the theatre of their first 
state of existence, from the voracity of fishes, or the more ra- 
pacious larvae of its own tribe, until the included eggs are 
hatched and emerge from their curious cradle.” Figures 12 
to 1 6 in Lesser’s Lyonnet represent H. piceus in its different 
stages. 
The perfect insects appear to be more abundant in the 
neighbourhood of London than in the country, and may be 
found during the whole year under weeds, &c. in ponds and 
ditches. I have taken the larvae at Whittlesea Mere, and the 
beetles near Norwich ; and for very fine specimens I am in- 
debted to Mr. John Atkinson, of Grove-end, who took them 
near the Regent’s Park. 
The plant is Poa ( Triodia Brown) decumbens (Decumbent 
Meadow-grass). 
