DYTICUS DIMIDIATUS. 
Order Coleoptera. Fam. Dyticidae Leach. Hydrocan- 
thari Lat. 
Type of the Genus Dytiscus marginalis Linn. 
Dyticus Geoff., III., Lat., Leach . Dytiscus Linn., Fab., Gyll. 
Antennae inserted close to the eyes at the base of the mandibles, 
subsetaceous, naked, 1 1 -jointed, basal joint the longest, 2nd very . 
short, 3rd and following clavate decreasing in length to the ter- 
minal joint, which is slightly curved and truncated obliquely 
(fig- 6)- 
Labrum transverse, slightly emargin ate, ciliated in the middle (1) . 
Mandibles short, robust, emarginate at the apex, which is trun- 
cated obliquely (2). 
Maxillae small, bent, acute, ciliated internally with bristly spines. 
Palpi ; internal short, 2-jointed, 1st joint shorter than the 2nd, 
which is slightly curved : — external long, 4-jointed, 1st joint 
small, 3 following long, of nearly equal length, subclavate, ter- 
minal joint truncated (3). 
Mentum transverse, bilobed, with the centre slightly produced 
and emarginate. Palpi arising from a cylindric scape, 3-jointed, 
1st joint minute, 2 following long of equal length, clavate trun- 
cate. Labium large, quadrate, ciliated (4). 
Head rounded. Thorax transverse. Scutellum distinct. Elytra con- 
vex ovate, smooth in the males, sulcated in the females. Wings 2. 
Tibiae spurred, anterior short. Tarsi 5 -jointed, anterior patellform, 
with suckers beneath and ciliated in the males ; 2nd pair with the 
3 basal joints dilated , with suckers beneath in the males (5 *) ; pos- 
terior elongated. Claws simple , of equal length, small in the pos- 
terior pair. 
Dimidiatus III. Mag. 3. 155. 3. Gyll. Ins. Suec. t. 1. p. 469. n. 4. 
Male smooth, shining, olivaceous -brown. Clypeus, palpi, a 
band between the antennae, sides of the thorax, margins of the 
elytra, and an oblique line near their apex ochraceous j an angu- 
lar mark between the eyes, anterior margin of thorax, antennae 
and legs ferruginous, the antennae at their base and the anterior 
legs being paler, the former with the 3 first joints robust. Thorax 
with a channel down the centre. Elytra with 3 longitudinal 
punctured striae on each, obtuse, depressed and punctured at 
the apex. Lobes of the sternum beneath divaricating, obtuse. 
Female: Thorax minutely punctured. Elytra with 10 deep chan- 
nels on each, extending scarcely beyond the middle, the re- 
mainder punctured. 
In the Author's and other Cabinets. 
