252 On Aquatic Carnivorous Coleoptcra or Dijtiscidce. 



The liind tibia is in the Noterides alone so long as or a little longer than the 

 femur, but is sometimes much shorter (Cybister) ; this part varies extremely in its 

 development ; in the feeble swimmers (Hydro vatini, &c.,) it is elongate, many times 

 longer than broad, and increases very slightly in diameter from the knee to the 

 extremity, a transverse section being nearly cylindric ; in the higher forms, the tibia 

 is much broader, and thousrh when dissected off it is found to be always narrow at 

 the knee, yet it attains its great breadth almost immediately below this, so that in 

 Cybister, the articular cavity is situated on an exti-emely short neck placed at the 

 anterior and outer extremity of the tibia; the tact that the greatest breadth of the 

 tibia is gained immediately at the knee is characteristic of the Cybistrini, and the 

 higher Hydaticides ; in the Dytiscini and Colymbetides, this abrupt spreading out 

 of the tibia immediately at the knee does not occur, but the tibia increases in 

 breadth by a gentle curve on its inner edge behind the knee, and gains speedily 

 its greatest width near to the base, thence continues nearly parallel sided to the 

 extremity, or indeed slightly diminishes in width towards the apex owing to a 

 slight curving inwards of its outer margin. In Bidessus and Sternopriscus, the 

 tibia is of peculiar form, being a little crooked owing to its being bent a little 

 outwards some distance below the knee, and a slight bending outwards of the tibia 

 likewise exists in many Hydro2Dorides, especially in Ccelambus. Usually three 

 faces are well defined on the tibia, viz. an upper, a lower, and an inner one, but 

 in Cybister where the metamorphosis of the tibia is extreme, the inner face has 

 entirely disappeared at the base, and is only tolerably well defined at the apex, 

 so that the tibia in such case forms a flattened upper face, and a curved or slightly 

 arched lower face ; and in Hydrocanthus the tibite are so flattened that they 

 form a plate whose two faces are only very slightly arched ; the lower face of the 

 tibia shows a varied sculpture, being sometimes polished and with only a series of 

 punctures placed near its outer edge (Noterides), sometimes dull and with a dense 

 series of sette running its whole length parallel with the outer edge (Vatellini and 

 many Hydroporini) sometimes densely punctate (Deronectes, group 1); but more 

 usually the interior portion of the face is smooth and polished, while the exterior 

 portion has large punctures bearing spines, (Cybister and many Colymbetides), while 

 in other cases these large punctures have to a great extent disappeared but leave 

 a marginal series along the outer margin; the outer and inner edges of the lower 

 face of the tibia are armed with a series of spines. 



The upper face of the tibia bears, quite at the outer edge, elongate fine cilire or 

 swimming hairs, which however are almost absent in Hydrovatus and Methles ; its 

 surface is, like the lower one, either polished or dull, but bears some large punctures 

 furnished with spines, which assume a very remarkable development in the higher 

 forms ; the usual arrangement of these spine-bearing punctures is that there is a 

 longitudinal series parallel with the outer margin, while the rest of the face external 

 to this series may be quite smooth (Ilybius) or bearing numerous large, irregularly 



