940 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



11. 14. — Group Thermonectini. (Vide p. 672.) 



This aggregate of the second degree consists of fortj-one species arranged in 

 four aofffreofates, and of two autooenera. The size of the individual is not less than 

 one-third and scarcely exceeds two-thirds of an inch of length ; the surface is nearly 

 always variegate, and may be punctate though it is generally very smooth and polished. 

 The antennal portion of the head is short, sometimes extremely short, and the eyes 

 are large. The thorax is destitute of a lateral margin ; the prosternal process is 

 short and obtuse or rounded at the apex, and is received into a broad, short, 

 shallow impression on the apex of the inter-coxal process of the metasternum, the 

 middle cox£e being always somewhat widely separated. The hind coxsb are 

 extremely large, their upper border is greatly arched, and never separated by a 

 long space from the middle coxse, and often very closely approximated thereto ; 

 the metasternum very elongate in the middle, terminates on each side as a slender 

 side wing deflexed for a considerable distance outside the coxa, the band so 

 formed is a little broader just before its termination than it is a little distance in 

 front of that point ; the suture between the wing of the metasterrmm and the 

 episternum (tliat is the piece at the outer anterior part of the breast) is very 

 distinctly curvilinear ; and the most internal portion of the metathoracic 

 epimeron may frequently be distinguished, even when the wing cases are quite 

 closed, as a small angular piece, whose inner angle nearly touches the terminal 

 angle of the side wing of the metasternum behind the a^iex of the episternum : as 

 however the sutures between this epimeron and the adjoining pieces are very 

 obliterated, it easily escapes observation even when really exposed. 



The coxal lines are always small, and sometimes quite obliterated, and even when 

 most developed their anterior part is always very far indeed from attaining the 

 anterior border of the coxa ; the supra-articular border when it can be distinguished 

 is never ver}' narrow, and is frequently so broad that it forms nearly one half of the 

 coxal lobe. The swimming legs are always highly developed ; the upper face of 

 their femora is either smooth and polished, without any punctuation, or possesses 

 some isolated punctures placed in a transverse manner on the basal portion and 

 without any development of pubescence : the upper face of the tibia bears a short 

 series of contiguous punctures (4 to 7 in number) placed near the middle of the 

 limb in a transverse or obliquely transverse direction, each puncture bears a thick 

 seta or spine bifid at the extremity ; the tibia bears at the apex two rather slender 

 spurs, each of which when viewed in a certain direction is seen to have its apex not 

 quite pointed but more or less minutely emarginate, though viewed in another 

 direction the spur may appear quite acuminate. 



The aggregate is a perfectly natural one, distinguished by the form of the epi- 

 siernal suture and the bifid extremity of the posterior tibial spui's; its curved epi- 

 sternal suture is present in the adjoining Eretes, but the bifid extremity of the 



