POLYMORPH A. 
281 
insects. The pupa is in a papery cocoon fixed to water plants. The 
adult lives on the surface of the water, the broad paddles propelling it 
swiftly along the surface, where it feeds on small insects which it finds 
near the margin. Numbers may be seen on the margins of fairly still 
water, continually describing complicated movements together ; when 
alarmed, they plunge below the surface of the water, carrying a bubble 
of air attached to the hind end. Some species are confined to smooth 
still water, others to swift mountain streams. All are unable to walk 
on land and they are found away from water only when flying at night, 
when they come to light. The family has no economic importance 
and has been little studied ; nothing is known of their hibernation, 
enemies and the like. 
Regimbart’s latest monograph (Genera Insectorum) enumerates 34 
Indian species, in the genera Dineutes (4), Aulonogyrus (1), Gyrinus (2), 
Orectocheilus (27). Orectocheilus gangeticus, Reg., is the common plains’ 
species, a medium sized black species found abundantly at the margin 
of rivers. Dineutes indicus , Aube., is a larger insect found on streams 
and stagnant water both in the plains and in the hills. 
POLYMORPHA 
If we omit the large distinct, series of beetles the Lamellicornia, 
Adephaga, Phyiophaga , RhynchopJiora and Heteromera , there remains 
a great assemblage of beetles, many of which fall into well marked 
families, but a proportion of which are extremely difficult to unite 
into natural families. Especially is this the case with the numer¬ 
ous forms which live in decaying wood, under the bark of trees, or in 
mushrooms; these beetles are imperfectly known, their structural charac¬ 
ters are very varied and no simple and accurate method of classing them 
has yet been arrived at, largely through the fact that but few are known. 
This, while true of these insects as a whole, is still more the case with 
the Indian forms, of which scarcely anything is known. Nominally these 
beetles fall into two series, those with antennae distinctly clavate, those 
with antennae distinctly serrate ; but many which have other structural 
affinities with one series have not clubbed or serrate antennae : their tarsal 
characters vary in even what are regarded as the limits of a family 
or sub-family ; and actually many families are characterised by such a 
number of characters relating to the trophi, antennae, coxae, tarsi, ven¬ 
tral abdominal segments and the like that the diagnosis to be of any use 
must be extremely full and detailed, occupying far more space than is 
