DYTISCUS. INSECTS. 255 



B. Exterior palpi thickest at their extremity ; anterior tarsi folding under the leg ; 

 body very gibbous. 



Gen. HYGROBIA. 



2. The four anterior tarsi with but four distinct joints, the fourth concealed by the 

 preceding, and this and the first two broad, with a brush below. 

 Gen. HYPHYDRUS, HYDROPORUS. 



II. A plate in the form of a shield at the origin of the posterior feet ; antennae of 

 ten joints, inserted between the eyes, and distant from the labrum ; exterior pal- 

 pi subulate. 



Gen. HALIPLUS. 



Gen. DYTISCUS, Lat. 



Body oval ; six palpi ; antennae with eleven equal joints ; tar- 

 si with five distinct joints ; the three first joints of the two 

 anterior tarsi forming an oval palette. 



The Dytisci have an oval body, more or less oblong, with the elytra hard, gene- 

 rally smooth in the males, furrowed in the females, and two membranous wings. 

 The thorax is broader than long, and notched anteriorly ; the head thick, and part- 

 ly sunk in the thorax; the antennae filiform, a little longer than the thorax, and 

 composed of eleven joints ; the mandibles thick, arched, and terminated by two 

 or three unequal teeth ; and the jaws corneous, pointed, and strongly ciliated. The 

 Dytisci are truly amphibious ; for though they live principally in the water, they 

 have also the faculty of going upon land and flying in the air. They swim with 

 much celerity, and are carnivorous. The larvae have a long and tapering body 

 of eleven segments, the first nine of which are covered with scaly plates for half 

 their circumference. The two last segments, the tenth and eleventh, form together 

 a long cone with a truncated point. The head is large, oval, covered with a scaly 

 plate, and furnished with two curved mandibles. On each side are five or six black 

 tubercles, which have been taken for eyes. The larvae leave the water at the period 

 of their transformation, and conceal themselves in the ground. 



D. latissimus, Lin. Blackish hrown above, chestnut helow; tho- 

 rax margined with yellow ; elytra dilated exteriorly, with a yel- 

 low border, and furrowed in the female. About an inch and a 

 half long. Inhabits Northern Europe. Lat. Gen. i. 229. 



D. marginalis, Lin. Elytra not dilated, with a yellowish border ; 

 thorax margined with yellow ; body blackish green above, yel- 

 lowish brown below, mixed with blackish ; elytra furrowed in the 

 female. 11 lines long, Inhabits Europe. Shaw, vi. pi. 33. 



D. Rceselii, Fab. Narrower, more oval and more depressed than 

 the preceding j exterior margin of the thorax and elytra yellow- 

 ish, and finely striated in the female. Inhabits France and Ger- 

 many. Oliv. Coleop. iii. pi. 3, fig. 21. 



D. sulcatus, Lat. Head yellowish before, black at its base ; tho- 

 rax black, with the margin and a band in the middle yellow; ely- 

 tra obscure, bordered with yellow, dentated and dotted in the 

 male, furrowed in the female ; under part of the body blackish. 

 Inhabits Europe. Oliv. Coleop. iii. pi. 4, fig. 31. 



Gen. COLYMBETES, Clairville, Dytiscus, Fab. 

 Body oval ; the four anterior tarsi in the males with their three 

 first joints equally dilated, forming a square palette ; antennae 

 the length of the head and thorax. 



