928 On Aquatic Carnivorous Coleoptera or Dytiscide. 
points as above mentioned, while the lower forms have become nearly or quite 
extinct. Hyphydrus is the highest form by far, and it is rich in species, while the 
remaining fragments indicate that the ancestors were probably more numerous in 
species. I should expect that we may find that Dytiscidee with similar posterior 
articular cavities, but with smaller coxee and less developed swimming legs, have 
existed at a past geological epoch in South Africa. 
It seems clear that South Africa is the metropolis of the Hyphydrini, all the 
fragmentary forms are found there, and there only ; and although the highest form, 
Hyphydrus, is widely distributed, yet the distribution is such that South Africa 
may be said to be its centre. No species is known from the western hemisphere. 
I. 9.—Group Hyprororini. (Vide p. 389.) 
This éxtensive secondary aggregate or group comprises ten genera and no less 
than three hundred species. They are small insects, the largest size attained being 
about 6 m.m. of length: the surface is always more or less punctured, and frequently 
bears a delicate pubescence. 
The prosternal process is attenuate and acuminate towards the apex, and never 
has a truncate hind margin; its apex always attains the intercoxal process of the 
metasternum. ‘The mesosternum is always placed at a considerable angle to the 
metasternum, so that it is but little visible between the prothorax and metathorax. 
The hind coxal cavities are either contiguous or approximate, never widely separate; 
the coxal process always shows an outer angle, (or more or less rudimentary lobe) 
projecting over the coxal cavity, so that this latter is neyer placed conupletely 
external to the coxal process. The hind margin of the posterior coxa is free, and 
not soldered to the ventral segments. The epimeron of the mesosternum is never 
reduced to a linear band. The scutellum is invisible although a minute portion of 
its apex is occasionally exposed. 
The large number of insects connected by these characters show a great deal 
of variation in different points of their structure; indeed there is scarcely any part 
of the external skeleton that remains unvaried throughout the aggregate. Never- 
theless by its positive and negative characters it is a perfectly distinct group in the 
Hydroporides. The coxal processes never show the two widely separated coxal 
notches with a largely developed extra-rimal lobe, such as is seen in the Hydrova- 
tini; and the ventral segments are not soldered with the coxe as in Bidessini. 
While from the Hyphydrini the group is distinguished by the coxal cavities never 
being quite exposed and much separated. Sternopriscus again has the mesosternum 
very invisible, and with a very narrow, sublinear epimeron. 
The genera, with one exception, have the fork of the mesosternum unconnected 
with the intercoxal process of the metasternum, and thus form an exception (but. 
not an unique one) in the Dytiscide, the vast mass of species of the family having 
these two parts connected, 
