On Aquatic Carnivorous Coleoptera or Dytiscidce. 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 coxae is 

 not quite so short as in Laccophilus, and the coxae 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 coxae 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 are in Laccophilus. The hind coxse 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 tibiae 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 ci-eature, is found in Madagascar and Zanzibar. 



TBANS. HOT. DUB. SOC, N.S., VOL. II. i Q 



