20G On Aquatic Carnivorous Coleoptcra or Dytiscidce. 



the anteuna is situated on it, and in front of the cavity the side of the clypeus i^ 

 likewise a little infolded ; in the case of Eretes (and in a less striking manner in 

 the other Hydaticides) where the eyes are lars-e, and the anterior parts of the head 

 are very much reduced in size, the antennte are inserted rather on the upper than 

 the under surface, the antennal cavity being quite visible from the front and above, 

 owing to the diminution in size and the comparatively slight folding of the front 

 angle of the epicranium ; on the other hand where the front of the clypeus is deflexed 

 or inflexed, as in Hyphydrus, Qiieda, Hydrovatus, Pachydrus, the antennal cavity is 

 situated quite on the undersurface of the head, the point of insertion being invisible 

 when the insect is looked at from the front and above. The surface of the eye 

 likewise is curved downwards, and continued on to the undersurface of the head so 

 as to form a considerable portion of its area; between its inner termination and the 

 elongate maxillary cleft of the buccal cavity there intervenes a naiTow space, 

 with a very polished surface, which serves as a groove for the lodgment of the base of 

 each antenna when these organs are placed in repose on the under surface of the head. 

 The gula (piece basilaire of the French authors) is broad and distinct, each of the 

 sutures separating its sides from the epicranium, terminates as in the Carabidte, in 

 front by a deep impressed puncture ; this puncture is placed at a considerable distance 

 behind the mental suture, and from it there is directed outwards a fine but 

 distinct suture, extending as far as the maxillary cleft ; in this manner a large 

 transverse piece is situated behind the meutum, but this jnece in the middle is not 

 separated from the gula by any suture, and it is doubtful whether it should be 

 considered a lateral exjiansion of the front of the gula (which in such case is T 

 shaped) or as a submentum (piece prebasilaire of the French authors) : this same 

 formation exists in the Carabidse, but is there excessively obscure owing to its 

 being of smaller size, and limited by more or less obsolete sutures.* 



Behind the eye there is a transverse suture or mark, which is clearly the 

 remnant of the suture seen in the Carabidte as separating the epicranium from the 

 protocranium : in a few cases this suture is very obsolete, thus in Dytiscus 

 duodecimpustulatus (No. 462) it can scarcely be traced : it occupies much the same 

 position in relation to the hind mai'gin of the head as it does in Carabidfe, but is 

 much nearer to the anterior part of the head than it is in that family, though it is 

 more than probable that there exists much difference amongst the members of the 

 Carabidse in this respect ; indeed T find that in Carabus violacens, the suture in 

 question is much nearer to the front that it is in Harpalus caliginosus. The 

 relations of the parts near this suture may be summed up by saying that in the 

 Dytiscidse as well as in the Carabidse the cheek is separated from the temple by a 

 transverse suture, but that the cheek is very much shorter in the Dytiscidae than 



• I believe myself that this transverse front bar of the gula is quite liomologous with the submentum 

 (piece prebasilaire) of some other Coleoptera. 



