On Aquatic Carmvorous Coleoptera or Dytiscide. 843 
the upper surface of the hind femur ; this structure is more developed in the male 
than in the female, and is indeed entirely wanting in the latter sex of certain 
species in whose male individuals it is conspicuous. It exists in various states of 
delicateness, and certainly the sound produced must be at the best very feeble, 
probably inaudible to the human ear, while in certain species where the apparatus 
is extremely fine it seems to me impossible that any sonorous vibration could be 
produced capable of affecting a nerve, unless this be assisted by a highly 
developed apparatus equal even to that of the human ear. 
The species of Laccophilus are distributed over all the warmer and temperate 
parts of the world, except the Pacific Islands and New Zealand; the stridulating 
species are confined to the New World with the solitary exception of the European 
Dytiscus interruptus, and it is quite probable that this species ultimately may be 
found to be also a North American one. 
I. 15.—Genus NEPTOSTERNUS. (Vide p. 317.) 
Under this name I have isolated a single species, in many points closely allied to 
Laccophilus but in others singularly different therefrom ; it is an insect of polished 
surface, of the size, and with much of the appearance, of a Laccophilus, of a yellowish 
colour, with the elytra dark, marked with large yellow marks: the thorax has an 
obscure marginal series of punctures in front, the ventral segments are destitute 
of scratches. 
The broad head is moderately elongate, and the eyes are placed so that a consider- 
able space separates their hind margin from the front margin of the prothorax. The 
outline of the thorax and elytra is perfectly continuous, and the hind angles of the 
thorax are much prolonged backwards so that they are extremely acute, in fact 
they form a long slender spine ; the hind margin of the thorax in the middle is 
straight not accuminate as in Laccophilus; the prosternum in front of the coxe is 
not quite so short as in Laccophilus, and the coxe are not so approximate, while the 
prosternum behind them expands into a trispinose process, the middle spine of which 
is longer than the two lateral ones ; the front coxe are very small. The wings of the 
metasternum are excessively slender, the hind coxa being in fact very little separated 
from the middle coxa ; these are more widely separated by the inter-coxal process 
than they arein Laccophilus. The hind coxe though large are not so enormous as 
in Laccophilus, and their front border forms a very much flatter arch. The coxal 
lines are strongly elevated and remarkably distinct ; the swimming legs are more 
slender than in Laccophilus ; the spurs of their tibize are slender and very acuminate, 
and the lobing of the joints of the comparatively slender tarsi is much less distinct 
than it is in Laccophilus. 
This, at present isolated creature, is found in Madagascar and Zanzibavr. 
TRANS. ROY. DUB. SOC., N.S., VOL. II. 5Q 
