On Aquatic Carnivorous Coleopiera or Dytiscide. 831 
record, when they were in a stage of evolution more primitive than that of any 
Carabide now remaining to us. Embryological studies may here give us 
important assistance. 
The following brief recapitulation will show the justice of this assertion. It has 
already been shown by Schaum and others that Pelobius has the head of Carabide, 
besides this its antennee approach more nearly to those of the Carabidz than to 
those of any Dytiscide, except the spurious Dytiscid, Amphizoa : the prothorax is 
quite that of Carabidze, except that the prosternal process connects with the metas- 
ternum and even this character is not foreign to Carabidze. (Compare Cyclosomus). 
The mesosternum is absolutely that of one division of Carabide. 
The metasternum is that of Carabidze, and possesses behind the transverse suture 
that exists in the majority of Carabidze, but in no Dytiscide, except the spurious 
Dytiscid, Amphizoa. 
The hind coxz are those of Carabidze, with some slight modifications, viz., that 
they are a little increased in size, that their internal lamin are accurately co- 
adapted (instead of touching only at one point), and that they are marked by an elon- 
gate excision for the play of the swimming leg, permitting cf a greater movement of 
the trochanter in one direction. 
The legs are those of Carabidee except that they bear ciliz. 
The general form is foreign to Dytiscide, for it is tub-like and does not show that 
evenness of outline conspicuous in the water beetles; the sculpture too is that of 
Carabide rather than that of Dytiscide. 
It seems clear then that Pelobius cannot be satisfactorily classed with the 
Dytiscidse ; and it is equally clear that it is a Carabideous insect having consider- 
able modifications to adapt it to move in water. 
It is therefore only included provisionally in my classification of Dytiscidee. 
Although I think Pelobius may be admitted among the Carabide, it will be there 
an absolutely isolated form. In the present state of knowledge of organic nature 
no animal having any affinity whatever to these three species can be pointed out. 
The isolation of Pelobius and the geographical distribution of its component three 
species are in themselves facts of much interest, for it is almost impossible to suppose 
that there can have been developed both in Europe and Australia absolutely ab 
4nitio animals which, notwithstanding their widely different environment have 
evoluted into a similar form which is absolutely isolated from all other known forms. 
It is almost impossible to suppose this, and we cannot but believe that the European 
species and the Australian species lived during the greater part of their ancestral 
record side by side, and only became separated from one another when their present 
structure was comparatively nearly established. It being then quite probable that 
the Australian species and the European species formerly had a common habitat, it 
will be an interesting question to consider at what period of the world’s history this 
could have been the case. Huxley has already suggested an answer to this question 
