INSECT A. 543 



In Orectochilus (Gyrinus villosus FABB., STUBM Deutschl. Ins. x. Tab. 

 227) the outermost palpiform lobe of the under-jaws is wanting, and thus 

 they have only one feeler. So also in many large exotic species. Hence 

 this character of the family is not constant, but the agreement of habitus 

 does not permit these species to be placed elsewhere. 



B. Abdomen composed of seven segments, the first three connate. 



Dytiscus L. (exclusive of the Hydrophili, Dytiscus GEOFFR.). 

 Antennae longer than head, filiform or setaceous, with eleven joints. 

 Eyes marginal. Head retracted within thorax as far as the 

 posterior margin of eyes. Posterior coxae ample. Maxillae arcuate, 

 acuminate ; external maxillary palps with last joint oval, larger, 

 thicker or truncated. 



Compare G. F. EBICHSON Genera Dyticeorum Berolini, 1832 ; ejusd. Die 

 Kdfer der Mark Brandenburg, I. p. 140, &c. 



A. All the tarsi with five joints, anterior of males patellate. 



Dytiscus CLAIRV., nob. (Sub-genera : Cybister CUKTIS, Acilius 

 LEACH, Hydaticus LEACH, Dytiscus LEACH, ERICHS.) 



Sp. Dytiscus marginalis L., RCESEL Ins. n. Ins. Aquat. Cl. i. Tab. i, LYONET 

 Ouvr. posth. PI. xi. figs, i 8, STURM Deutschl. Fauna, Ins. vin. Tab. 185, 

 1 86, DEJEAN et AUBE, Iconogr. et Hist. not. des Coleopt. $ Europe, Tom. v. 

 PI. 5, figs. 3, 4; 15'" long, feet and body red-brown, thorax and shield- 

 covers gleaming black, a yellow-brown border along all the sides of the 

 thorax and along the outer edge of shield- covers ; the female (Dytiscus 

 semistriatus L.) has longitudinal furrows on the shield-covers more than half 

 their length. The females also of other species are distinguished by simi- 

 larly striated elytra, although in some of these females with smooth shield- 

 covers occur. The first three joints of the tarsi of the fore-feet form in the 

 male a round disc which is haired on the margin, and supplied with suckers 

 below. Dytiscus (Acilius) sulcatus L., PANZEB Deutschl. Ins. Heft 31, 

 Tab. 9, 10, STUBM 1. 1. Tab. 189, &c. 



The larvae of these water-beetles have a large oval head, armed with 

 strong curved jaws, three pairs of thin haired feet, and two appendages at 

 the hind part of the body subservient to respiration. They are very vora- 

 cious, and like the larvae of libellae are incessantly on the hunt for other 

 water-insects. The nymphs lie concealed in the ground under the water. 

 The perfect insects breathe on the surface of the water, by extending the 

 abdomen above it, and raising the shield- covers a little, whilst the head 

 is kept under. 



The intestinal canal does not undergo any remarkable change in the 

 metamorphosis. The four vessels that secrete urine are especially long, 

 the rectum has a lateral appendage, membranous and folded. Below the 

 rectum are the openings of vessels which secrete a milky fluid. KAMDOIIR 



Abhandl. iib. d. VerdauungswerTcz. s. 79 82, Tab. n. figs, i 5, LEON 



DUFOUB, Ann. des Sc. nat. in. PL 10, fig. 8. 



