924 On Aquatic Carnivorous Coleoptera or DytiscidoB. 



may be due to the similarities of environment which the two insects alluded to have 

 lonsr had in common. 



The Laccophilini occur probably in all warm and temperate regions except the 

 Pacific Islands and New Zealand ; Neptosternus has been found only in Madagascar 

 and Zanzibar, and it is probable that other species will be detected in the great 

 African island. 



Only highly developed forms exist in the Laccophilini, at present we are quite 

 unacquainted with any more primitive forms of the group. Of the two genera 

 forming it, Laccophilus is undoubtedly however a more perfect form than Nepto- 

 sternus, and is indeed entitled to a high place as being amongst the most perfectly 

 organized of the Dytiscidae. Neptosternus though inferior is itself an extremely 

 evoluted and specialized form. 



The group is widely distributed in the globe, but wanting in the Pacific Islands 

 and New Zealand, and very sparsely represented in the cooler regions of the world 



II. 6. — Group Hydkovatini. (FicZe p. 320.) 



This aggregate of the second degree is formed by one genus of numerous species, 

 and an autogenus : the greatest size attained is 6 m.m. of length and this is only 

 by a single species, the others being usually much smaller than this. The form is 

 short and convex, the base of the thorax is very accurately coadapted with the 

 wing-cases. The hind legs are very feeble, their articular cavities are concealed, 

 but are not contiguous, being separated by an intra-rimal space marked off exter- 

 nally by a very distinct coxal notch, outside this coxal notch the coxal process 

 projects as a prominent free lobe. The anterior border of the hind coxee is but 

 little arched ; and the intermediate coxae are widely separated. The prosternal 

 process is broad and short, and is broadest behind, showing in fact a nearly straight, 

 or truncate, hind border. The mesosternal fork is largely connected with the 

 iutercoxal process of the metasternum. The scutellum is quite invisible, and only 

 four joints can be detected on the front and middle tarsi. 



The peculiar structure of the coxal processes, when once appreciated is found to 

 be very characteristic ; it will be noticed that the articular cavities of the hind legs 

 are broadly separated by a piece (or rather by two conjoined pieces) adpressed to 

 tlie level of the ventral segments, and outside of this part the coxal cavities have 

 a visible opening, which is in fact their inward termination ; the whole of the 

 articular cavity except this internal opening is protected by a well developed free 

 process placed outside the coxal notch; thus when the insect is in the natural 

 position (ventral surface downwards) the base of the trochanter moves over the 

 extra-rimal portion of the coxal process, while the coxal notch and the adpressed 

 intra-rimal portion allow the trochanter, when extended as far as possible in the 

 posterior direction, to become free and move on the face of the intra-rimal portion. 



