238 On Aquatic Carnivorous Coleoptera or Dytiscide. 
condition, Hydroporus gigas No. 427 (Chostonectes) may be mentioned. In Pelobius 
and the Hydrovatini we have another form of articulation of the swimming leg ; 
inasmuch as the coxal cavities are rather widely separated, but yet are concealed 
by a coxal lobe; the inner termination of the articular cavity appears therefore in. 
these cases in the form of an opening or excision on the hind margin of the internal 
lamina. I have already spoken of a mark which commonly exists on the hind 
margin of the internal lamina, either as a slight notch or interruption of the outline 
of the coxal process (Cybister, Ilybius, &c.,) or as a closed short suture (Dytiscus). 
This coxal notch is remarkably persistent, and indeed though it appears to be absent 
in many forms (Acilius e.g.) yet on careful examination I have always found some 
traces of it, it exists also in the Carabidze, and is perhaps an indication that this 
part of the coxa is formed by the coalescence of two distinct pieces ; its persistence 
is at any rate very remarkable, and is clearly an indication of some formerly different 
structural condition of these parts. I had thought at first that the articular opening 
existing in Pelobius and Hydrovatini was merely an enlargement of this coxal notch 
but such is not the case, for in Pelobius the coxal notch may be seen existing on 
the coxal process, just outside the articular openmg. In the Noterides the coxal 
lobes are of large size and peculiar form, reaching furthest backwards at their outer 
angle, which is thus more or less acute, they are greatly prominent from the rest of the 
under surface, and thus form a deep elongate axilla, while the articular cavities them- 
selves are completely concealed ; in respect therefore of the development of the 
coxal processes, and concealment of the articular cavities, the Hyphydrini and the 
Noterides stand as the opposite extremes of the family. In Amphizoa the articular 
cavities are widely separated, and are concealed, but their inner termination is 
distinctly visible on the hind margin of the coxal process, the coxal notch being placed 
immediately outside of this opening: this differs from the articulation in Pelobius, 
inasmuch as the termination of the articular opening is not prolonged forwards, 
and thus formsa shallow emargination instead of a deep excision, if we suppose the 
space separating the two cavities in Amphizoa to be absent, the structure would 
not then differ materially from what exists in the Macro-Dytiscide. 
The structure of the hind coxa in the Dytiscidee may be summed up as differing 
from that of the Carabidze in the following points; 1. The large size or area of the 
external lamina; 2. The arched anterior border of this part; 3. The accurate adap- 
tation and soldering of the two internal laminz together by a straight and perfect 
suture; and 4. The contiguity of the articular cavities. As regards the first of these 
points, it is certain that so far as the large majority of the Dytiscidee are concerned, 
the greatly increased size of the outer lamina of the hind coxa is very remarkable 
and is one of the modifications of structure most characteristic of the family : it is 
however only a question of degree, and varies extremely in the different groups, so 
that Amphizoa and Pelobius, in which forms it is smallest, appear rather to be 
Carabidee than Dytiscidze in respect of this peculiarity : I am not aware however of 
