924 On Aquatic Carnivorous Coleoptera or Dytiscide. 
may be due to the similarities of environment which the two insects alluded to have 
long 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 Dytiscide. 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 Hyprovari. (Vide 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 coxe is but 
little arched ; and the intermediate coxee 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 
intercoxal 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 
the 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, 
