BYTICIDiE. — DYTICUS. 89 



Very similar to the preceding, but known at once by its yellowish scutellum, 

 form of the sternal lacinise, &c. : oblong-ovate, rich olivaceous, or olive-black: 

 head as in the last, but the frontal lunula generally more distinct: thorax 

 broadly margined throughout with yellowish, the posterior border rather 

 undulated, and somewhat narrowed, the disc with an abbreviated dorsal line, 

 and the anterior margin with a series of impressed dots, the lateral and 

 posterior margins nearly impunctate: scutellum with its centre, and some- 

 times its apex, flavescent : elytra oblong-ovate, very little dilated, the lateral 

 margin broadly flavescent; the disc with three punctate striae, the spaces 

 between with a row of very remote, rather obsolete, impressions, and the apex 

 with some scattered ones : body beneath bright testaceous-yellow, the sutures 

 of the breast and the margins of the abdominal segments black : legs testa- 

 ceous ; the posterior, with the apex of the tibia? and the tarsi, pitchy-black. 

 Female with the thorax and elytra above thickly punctate, the latter deeply 

 sulcated beyond the middle. 



Common in ponds round London; apparently rare elsewhere. 

 " I never could detect this insect in Cambridgeshire." — Rev. L. 

 Jenyns. " Lawrence Waltham." — Mr. Hanson. 



Sp. 5. marginalis. Olivaceo-nigricans, thoracis limbo elytrorumque margine 

 luteis, elytris posticis latioribus undique punctulatis, intra apicem lunula Jla- 

 vescente, sterni laciniis subacutis. (Long. corp. 1 unc. 1 — 4 lin.) 



Dy. marginalis. Linni. Don, iv. pi. 161. Steph. Catal. p. 62. No. 627. 



Oblong-ovate, elytra dilated behind the middle : head smooth glossy-black, with 

 the labrum and anterior edge luteous, a triangular mark on the forehead 

 rufous, and a slightly-elevated line on the crown : thorax rather arcuate be- 

 hind, moderately convex, the disc glossy-black, with an obsolete dorsal chan- 

 nel, the margins entirely luteous, with an impressed punctulate stria: scutellum 

 black: elytra anteriorly convex, nearly smooth, posteriorly depressed and 

 punctate, the disc with three punctate stria?; shining olive-black, with the 

 lateral margin broadly luteous at the base, and narrowly towards the apex : 

 body testaceous-yellow beneath, with the edges of the segments and middle of 

 the sternum dusky, the laciniae of the latter broad, lanceolate : legs pale-tes- 

 taceous. Female with the upper surface punctulated, the elytra deeply sul- 

 cated rather beyond the middle. 



The most abundant species of this genus in Britain, occurring 

 nearly in every pond and large expanse of water, throughout the 

 year, in common with several other Dyticidse. From the observa- 

 tions of Esper, this insect appears to possess considerable longe- 

 vity (unless life were protracted through celibacy in the instance 

 recorded by him) : he tells us that he kept one in a vessel of water 

 three years and a half, feeding it once a week, or oftener, with a 

 piece of raw beef, the juice of which it devoured with avidity: it 

 however occasionally fasted for a month. A specimen of Hydrous 



