212 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



The small amount of variation exhibited by the trophi throughout the family is 

 perhaps largely conuected with the different parts being thus closely packed 

 together. However this may be, the absence of any conspicuous developments of 

 the trophi is remarkable, especially when we recall the fact that these parts in the 

 Dytiscidce are extremely similar, except in some minor details, to those of the 

 Carabidoe, and remember the great modifications of these parts that the latter family 

 displays; ifthelabrum of Carabus, where the ligula is merely a small semi-mem- 

 branous piece connecting the anterior parts of the large paraglossfe, be contrasted 

 with that of Authia, where the ligula is a very large, elongate, horny lobe, at the 

 base of which on each side is attached the insignificant paraglossa, the great 

 difference here displayed will render very striking the uniformity of the correspond- 

 ing parts throughout the Dytiscidas. 



The parts of the mouth show no important differences from those of the Carabidae, 

 but there are two or three comparatively unimportant details as to which a suffi- 

 ciently constant di;i'erence exists to make them worthy of mention ; these are — first, 

 the complete absence of outstanding setae from the palpi or other parts of the 

 mouth : second, the fact that the second joint of the maxillary palpi is only about 

 equal in length to the third, whereas in the Carabidfe in the vast majority of 

 cases the second joint is considerably longer than the third; and, third, the deep 

 emargination of the extremity of the lower face of the supports of the labial palpi. 

 These characters are not, it will be admitted, of great importance, and as regards the 

 second of them it may be mentioned that, in the Pseudomorphini, the second joint of 

 the maxillary palpus remains, as in the Dytiscidse, scarcely longer then the third 

 joint. The undivided external maxillary lobe seen in Amphizoa is also paralleled 

 among the Carabidse (Callistus, and one or two other genera). 



The A^JTENN^ of the Dytiscidse are always eleven-jointed, and are usually slender 

 with the joints elongate, the second being, however, frequently shorter than the 

 others, and the joints from the third to the apex each a little shorter and more 

 slender than its predecessor. Although this is the structure in the larger and higher 

 forms, there is a considerable diversity in other parts of the family. The Noterides 

 are especially peculiar in this respect, their antennse, being short and more or less 

 distinctly incrassate in the middle ; in this group even when the antennae are 

 apparently .slender and simple as in Hydrocanthus, it will be found that the middle 

 joints (joints G to 8) are a little broader and longer than the following or than the 

 preceding ones. In the Hydroporides the rule is that the second joint is as long as, 

 or longer than the third, and the antennse are only as long as, or shorter than the 

 head and thorax, and not remarkably slender, while in the Hydi'ovatini and 

 Hyphidrini and Bidessini it is not unusual that they should be feebly serrate 

 internally. In the Colymbetides the antennae are slender and filiform or setaceous, 

 but never become very remarkable on account of elongation and tenuity, and in 

 the earlier genera of the group, are usually comparatively thick ; it is in the 



