On Agnatic Carnivorous Coleoptera or Dytiscidce. 223 



Hydrovatus, and the scatum is then very inconspicuous ; in Laccophilus especially 

 it appears as a short band in front of the scutellum without any division into two 

 lobes. I have already remarked that the hind margin of the scutum is impinged on 

 in the middle by what appears to be an angular prolongation from the front of the 

 scutellum ; this prolongation is however probably a distinct piece of the scutum, as 

 it certainly is in the Carabidre, in some members of which family (Harpalus 

 cahginosus e.g.) it appears as a large piece, nearly as large as the scutellum, reaching 

 quite to the front of the mesonotum, and thus widely separating the two lobes of 

 the scutum. The scutellum always comes to the surface of the body at the base of 

 the suture of the elytra, but is very frequently invisible (Laccophilus, Noterides, 

 Hydroporides and Methles) owing to its being covered by the middle of the base of the 

 prothorax; but in the Macro-Dytiscidre the scutellum is always visible. In the groups 

 where it is concealed it varies in form and size, thus in Noterus it forms a very short 

 broad triangle the apex of which is directed to the hind part of the body ; in 

 Laccophilus also it forms a short, broad triangle with rounded sides ; in Hyphydrus 

 it forms an irregular four-sided figure, broadest behind, the hind margin straight and 

 with projecting lateral angles ; in Hydrovatus it reaches its extreme diminution, 

 and can only be detected as a minute transverse raised band : in the other Dytiscidse 

 it has the form of a more or less elongate triangle, with the base in front attached to 

 the scutum, but the sides forming a free edge, under which lock the anterior parts of 

 the sutural edges of the wing cases. The post-scutellum is a transverse band on a 

 lower level than the scutellum ; on it rests the base of the wing case when closed, 

 and to its extremity is attached a small membrane ; this membrane is sometimes 

 ciliate at its edges (Dytiscus, Cybister) and is always present in the Dytiscidae, and 

 also in some Carabidse, though it has been supposed by Lacordaire (Introduction a 

 r Entomologie, I., p. 347) to be peculiar to Dytiscus. 



The most important piece of the mesosternum — the mesosternum proper or 

 medisternum — consists of a middle portion, giving off above a lateral branch on 

 each side, so that it may be roughly described as being somewhat T shaped ; the 

 middle portion is the lowest part of the mesosternum, and has more or less the form 

 (when disarticulated) ' of a short six-sided column, as seen in Dytiscus, Cybister, 

 and most of the larger Dytiscidse, but in the case of such of the smaller Dytiscidaj 

 as have only a very slight extension of the mesothorax in the longitudinal direction, 

 the columnar appearance is quite lost (Laccophilus, Hydrovatus, Hyphydrus, &c.), 

 and it is also but little conspicuous Avhen the depressed form of the insect causes 

 the column to be very short (as in Copelatus). Like the prosternum proper, the 

 medisternum appears to consist of two pieces placed one in front of the other, and 

 distinguished by a very prominent line of junction. The front of the column is 

 placed immediately behind the anterior coxse, and is on each side usually more or 

 less hollowed for their accommodation, so that in fact the column bears two facettes 

 in front which are sometimes separated by a channel (Cybister) ; in Dytiscus 



