234 iiYDROPHiLiD^. [HeJophorus. 



terminated by a perfoliate club, and the legs are rather long and slender ; 

 the under surface of the body is covered with a silky pubescence : the 

 Helophori cannot swim, but proceed along the surface of the water by 

 awkAvard movements of their legs ; in summer they often bury themselves 

 in the mud, but they are able to fly from one place to another if they 

 choose, when the pools they inhabit are dried up ; they are, however, 

 often found at some distance from any water, in moss or under damp 

 leaves, or even by sweeping herbage. 



The larva of Selophorus aquaticus {grandls. 111.) is figured by Schiiiite (L, PI. vii., 

 Fif. 5) : it is pale with the corneous parts fuscous; the head is small, much narrower 

 than the prothorax which is trapezoidal, slightly narrowed in front, and twice as long 

 as the meso- and meta-thor;is ; the scuta of the three thoracic segments are entire, and 

 cover the whole surface, and are deeply channelled longitudinally in the middle ; the 

 abdominal segments are nine in number, the first eight of equal breadth ; each of 

 these eio-ht segments is protected by four corneous plates arranged transversely, the 

 middle pair being the largest ; these are really formed by the breaking up of the 

 single scuta, and correspond to the minute plates on the abdominal segments of Hydro- 

 lius, Berosus, &c., that have been before referred to ; the ninth segment bears one 

 large plate ; from each side of the segments and from each portion of the scuta proceed 

 sino-le long setas ; the cei'ci are long and jointed, and each of them bears five or six 

 long seta) ; the legs are very short, and terminate iu simple claws. 



The genus comprises about sixty species, which are almost entirely 

 found in Europe and North America ; a few species, however, occur in 

 Northern Africa, Madeira, and the Canaries ; it is a great matter of 

 doubt how many species we really possess as British ; if we admit all 

 the described species the number will amount to eighteen, but five or 

 six at least of these appear to be varieties or races, so that the total 

 number does not actually exceed twelve : there is hardly any other 

 "enus that is involved in such confusion and causes so much difficulty 

 to Coleopterists ; in determining the exotic species the same difficulty is 

 also found ; there are, however, several well-marked groups and forms 

 that are very easy to determine ; in some, however, the synonymy is in 

 a state of hopeless confusion ; the student who wishes fully to study 

 the genus may consult with advantage the revision of the species by 

 Thomson (Skand. Col. x. 297) ; Bedel has done more than any other 

 Coleopterist of late years towards unravelling some of the difficulties. 



I. Alternate interstices of elytra tuberculate ; colour 

 shining black with aBueous reflection on elytra, thorax 



somewhat iridescent ■ . . . H. tUbebculatus, Gyll. 



II. Alternate interstices of elytra strongly raised in ridges ; 



colour brown ; thorax not metallic, 

 i. Humeral angle of elytra projecting ; ridges of thorax 



irregular, sometimes raised in small knobs; length 



5-5| mm ; . H. eugosus, 01. 



ii. Humeral angle of elytra blunt; ridges of thorax 



simply convex, not interrupted ; length 3-3^ ram. . H. kubilus, F. 



III. Alternate interstices of elytra plainly, but not 

 strongly, raised in riJges; thorax metallic; colour 



laj-own H- INTEEMEDIDS, Muls. 



IV. Alternate interstices of elytra not or very slightly 

 raised iu ridges; thorax metallic. 



