144 
BRITISH BEETLES. 
nearly always bears a little heap of dry mud or caked 
sand upon its back. When cleaned, the elytra exhibit 
very coarse punctuation for so small an insect. 
The ParniDjE are aquatic or sub-aquatic in their 
habits, and are divided into two sub-families, the 
Parnina and Elmina, both having the head received 
into a prolongation of the prosternum, and the anterior 
segments of the abdomen soldered together; differing, 
however, in their anterior coxae, which are cylindrical 
and transverse in the first, and almost globular in the 
latter. In the Parnina the body is clothed thickly 
with short hairs, and the second joint of the antennae 
assumes a widened, ear-like form : the species are 
found near or in running water, on stones or water 
plants. 
• The Elmina (which are much smaller) have the 
antennae very little thickened at the apex, no tooth to 
the mandibles (which are, however, bifid) ; scarcely 
any pubescence on the body, which is often metallic 
and frequently caked with dirt ; and the last joint of 
the tarsi very long, with exceedingly strong claws. 
They cling to the rough undersides of large stones in 
strongly-running waters, especially delighting in such 
as are under or close to a fall of any kind ; and may 
be found at a considerable depth from the surface. 
They are gregarious in habit, many examples of 
different species (or even genera) being sometimes 
found together. 
The Heteeocerid.®, comprising a single genus, 
Heterocorus, have the antennae short, the last seven 
joints forming a flattened club; the parts of the 
mouth not hidden, the ligula being very projecting; 
the legs adapted for digging, with four simple joints 
