Hi/drorharis.'] iiYDROriiiLin.r,. 221 



first seven abdominiil segments ; tlie corei are short bnt lonnfcr than in the larva; of 

 the snceeedinfj species : it is said that this hirva, wlien it lias seized its prey, raises it 

 by its inandibles out of the water in order to paralyze its resistance. 



According to M. Duineril the digestive canal in this and tlie preceding 

 species undergoes remarkable modifications during the ti'ansformations of 

 the insect ; in the larv.Te it is short and suited to their digestion as 

 carnivorous, hut in the perfect insect it becomes much elongated and 

 adapted to their herbivorous diet. 



HYDROBIINA. 



This triljc is composed of several ratlier M'idely differing genera, some 

 of which (e.g. Chajtarthria and I5erosus) miglit perhaps l;)e formed into 

 separate tril)e3 ; the species are of an oval or hemispherical form ; some 

 of them bear a superficial resemblance to those of the preceding trilie, 

 but they are all much smaHer, and none of them have tlie mctasternum 

 prolonged behind into a sharp spine ; one exotic genus (Amphiops) is, as 

 Dr. Horn points out, remarkable for having four eyes like Gi/rmus. 



Our genera may be classed as follows : — 



I. Fii-st and second ventral segments not covered by plates. 

 i. Ventral segments five (tip of sixth sometimes visible) ; 

 anterior co\al cavities open behind. 



1. Last ventral segment entire ; intermediate and 

 posterior tibia) without swiunning hairs on their 



inner border. 

 A. Antenna; 9-jointed. 



a. Length 4-8 mm.; maxillary palpi long. 



a*. Elytra with a distinct sutnral stria more or 

 less abbreviated. 

 af. Ma.xillary palpi with the last joint plainly 



longer than the penultimate Htdkobius, Lcacli. 



bf. Maxillary palpi with the last joint plainly 

 shorter than the penultimate, 

 aj. Base of thorax narrowly bordered ; inter- 



mediate and posterior tarsi 5-jointed . . rniLUTDUug, Sol. 

 bj. IJase of thorax without trace of bor- 

 der ; intermediate and posterior tarsi 



4-jointed . CVMBIODTTA, J]e(h'/. 



cf. Maxillary palpi with the last joint about 



equal to the penultimate ENOCimrs, Thorns. 



b*. Elytra without trace of sutural stria ; last 

 joint of antenna) plainly shorter than penul- 

 tinnite Hiclociiakes, Mul.s. 



b. Length not exceeding 3 mm. ; maxillary palpi 



short. 



a*. Upper surface metallic; base of thorax with- 

 out trace of border VwiXCYMVS, Thoma. 



b*. Upper surface not metallic ; base of thorax 



very narrowly bordered Anac.i:xa, Thoma. 



]?. Antenna' S-jointid Laccobivs, Er. 



2. Last ventral segniunt almost always emarginato ; 

 intermediate and posterior tibi;e furnished with 



swimming hairs on tlieir inner border Beuosts, Leach. 



