On Aquatic Carnivorous Coleoptera or Dytiscide. 239 
any Carabide, in which the area of the external lamina of the hind coxa is anything 
like as large as it is even in Pelobiusand Amphizoa. In Trachypachys and Systolo- 
soma of the Carabide, the hind coxa is large, but it is made so by the increase in 
size of the internal rather than of the external lamina. In Silphomorpha the in- 
ternal lamina is very small, and the external one correspondingly large, thus making 
a slight approximation to the Dytiscide. Second, As regards the arched anterior 
border of the hind coxa in the Dytiscidee ; such a character is I believe absolutely 
unknown in the Carabide, but unfortunately it is not always presentin the Dytiscide, 
being absent in Pelobius, Amphizoa, and Colpius, and very nearly absent in Suphis. 
Third, The accurate coadaptation of the two internal laminz at their junction on 
the middle line is quite characteristic of the Dytiscide and is always present ; it 1s 
however approximated by some Carabidee, viz., the Pseudomorphides, Trachypachys 
and Systolosoma; but the only one of these that really makes any near approach 
in this respect to the Dytiscide is Trachypachys. Fourth, As regards the contiguity 
of the articular cavities, this is very conspicuous and characteristic in the Macro- 
Dytiscidee, but in many other Dytiscide it is not present (Pelobius, Hydrovatini, 
Hyphydrini, Bidessini, Colpius), indeed a slight separation of the cavities is so 
common in the lower forms of the various groups, as to strongly suggest the idea 
that all the species of Dytiscidze have had ancestors with separated posterior coxal 
cavities like the Carabidee. 
The Haliplides show not the least approach to the Dytiscide in the structure of 
the hind coxee ; on the contrary they possess a peculiar development, which is not 
approximated by any Carabidee or Dytiscidee, of these parts. 
Hinp-sopy, or Anspomen.—The dorsal plates of the hind body are eight in number, 
and they differ but little from one another in length : they are membranous in tex- 
ture, but usually dark in colour ; the seventh and eighth are a little thicker than the 
others, and have thus a leathery consistence, and they are also dull and more or less 
punctate, especially the eighth, while those in front of them are shining : in Dytiscus 
the two basal segments bear a large quantity of very fine, elongate hair, and other 
genera show sometimes a similar development though to a less extent. In Hydro- 
vatus the dorsal plates are very thin and delicate, and pallid in colour, and the 
apical one differs but little from the others. The basal segment is attached to the 
hind margin of the metanotum, and each segment is attached by its sides, by the 
intervention of a very delicate membrane, to the harder side pieces of the body. The 
metathoracic stigma is placed at the hind margin of the metathorax, at the side of 
the body, and may be either small and inconspicuous (Cybister), or elongate in the 
transverse direction (Dytiscus) : there are seven pairs of true abdominal stigmata ; 
the first abdominal plate is without a stigma, but each of the other plates bears at 
the outside a stigma placed in its delicate membranous border, the stigma of the 
eighth or terminal segment, is usually placed quite at its front edge, but in Cybister 
is placed near its hind margin. The stigmata vary greatly in their size and develop- 
