21G 
BRITISH BEETLES. 
The species of Plectroscelis and Chsetocnema have 
their hinder tibiae armed with a tooth on the outer side 
below the middle; and Thyamis, a genus of large 
extent, may be known by the elongate basal joint of 
its hind tarsi, which is about half the length of its 
tibiae. Although its members are usually of dull- 
yellowish colours, there is one, T. dorsalis, of great 
beauty, being intensely black and shining, with the 
thorax and a broad sharply-defined margin all round 
the elytra bright yellow ; it occurs somewhat rarely at 
Mickleham, Weymouth, and in the Isle of Wight. 
Psylliodes is more robust, compact, and inclined to 
an elongate-oval in outline ; the basal joint of its hind 
tarsi is elongate, but differs from that of Tliyamis and 
its other allies in being inserted not at, but above the 
apex of its tibiae, which is sloped off : here, also, the 
antennas are more distant at the base. 
Of the remaining genera Apteropeda and Mniophila 
are conspicuous for their extreme rotundity and con- 
vexity ; A. graminis (Plate XV., Fig. 2), either bronze 
or bluish-green in colour, being abundant in autumn 
among all kinds of wild plants, and M. mvscorum , — 
more like a black seed, or a little round Acarus, than 
a Ilaltica , — occurring in moss in many localities. 
The Cassidina, or Tortoise-beetles, are entirely 
unlike any other British Coleoptera (except, perhaps, 
Thymalus limbutus), on account of their broad, flat- 
tened bodies. Their head is hidden beneath the 
thorax, which is semicircular, and overlaps the elytra ; 
the parts of the mouth are feeble, situated at the 
under-side of the head, and received at rest into a 
projection of the prosternum ; the antennas straight, 
short, and slightly thickened towards the apex, but 
