On Aquatic Carnivorous Coleoptera or Dytiscide. 895 
less conspicuous, setze ; the hind coxee are large, and the wings of the metasternum 
are deflexed outside them as slender nearly parallel-sided bands. The hind legs are 
rather slender, but their femora have a rectangular apical angle; their tarsi have 
no lobing of the joints externally and are terminated by two short, stout, very 
nearly equal claws. The male characters are highly peculiar; the front tarsi are 
not broad, but are incrassate and compressed, and bear beneath some pencils of 
long sets, mixed with which are three or four transverse series of small palettes, 
and they bear extremely long claws; the last ventral segment is marked by two 
very deep parallel lines running along its middle. 
This interesting and very rare North American insect, has no close allies, the 
peculiar coxal lines and processes, are not very different to what exist in Matus, 
but it 1s worthy of remark that it is the Australian, not the North American, 
species of Matus that most approach it. The male tarsi are an approximation to 
what exists in some Colymbetini, the peculiar Dytiscus pustulatus (No. 945), for 
example. 
I. 58.—Genus MATUS. (Vide p. 599.) 
Three species form this aggregate ; their individuals are of rather narrow parallel 
form, but a good deal attenuate behind, and with very broad head, The prosternum 
is sulcate along the middle, the groove extending from near the front margin of 
the prosternum to the apex of the prosternal process: the side of the prothorax 
has a raised margin. 
The middle coxze are rather widely separated, and the intercoxal process of the 
metasternum bears in front a highly developed cavity for the apex of the prosternal 
process. The hind cox are very large, and their front border approaches very 
close to the middle coxa, the wings of the metasternum are therefore very short, 
and greatly deflexed as slender bands outside the front part of the hind coxze, this 
band is in its terminal portion so excessively slender that it is truly an acuminate 
line ; the coxal lines are deep, and start in front from the apex of the metasternum 
and are parallel or subparallel till they approach the coxal lobes, and then are 
gently turned outwards, leaving a broad supra-articular border, The hind legs are 
well developed for swimming, being rather short and stout, and their tarsi are 
peculiar, the hind margins of the joints being well lobed externally ; but the lobe, 
or produced part, is here at the upper edge, whereas in the other genera where a 
lobing of this sort occurs it is at the lower edge of the tarsus; the two claws 
terminating the tarsus are straight, and slender, and very unequal in length, the 
outer one being about twice as long as the inner one. 
The surface is polished and almost without sculpture; the male tarsi are but 
little developed. 
The genus is again an isolated one; the species when seen from above suggest 
