On Aquatic Carnivorous Coleoptera or Dytiscidce. 8-19 



middle of the prosternum shows no [)erpendicular face in front in the middle ; the 

 pectoral prominence is very coarsely sculptured while the adjacent lateral parts are 

 smooth; the suture between the hind coxa and metasternum approaches near to the 

 middle coxa ; the coxal processes are highly developed and greatly prolonged be- 

 hind, the pi'olonged angles being rendered sharply acuminate by bearing some rigid 

 ciliae; the swimming legs are rather slender, the femora and tibiifi but little flattened 

 or laminate; the former bear a well developed group of cilioe at the extremity of 

 their hind margin; the tarsi are about as long as the tibiae, their basal joint as long 

 as, or longer than, the three following ones together. 



This genus has been mixed with Hydrocanthus, but was separated by Crotch so 

 far as regards the North American species; he suggested for it the name of Suphisellus, 

 but not in a formal manner — only as it were hypothetically, and I have thought it 

 oil the whole better to use a new name. 



It is very distinct from Hydrocanthus, by the small size, the greatly narrower 

 prosternal process, and the feeble swimming legs. 



The species seem to be found in the warmer parts of both hemispheres, but so far 

 -as yet known are absent from Australia. 



I. 10.— Genus H YDROCAN'THUS. {Vide p. 279.) 



This aggregate consists of about twelve species ; they are the most highly 

 organised of the Noterides, the size varies between 4 and 8 m.m. of length, the form 

 is somewhat elongate, very acuminate behind, very convex transversely above, the 

 surfiice is extremely polished, and is never variegate by spots or stripes. The 

 antennas are slender, and are rather short, the middle joints of the antennae often 

 distinctly a little longer than the others, but scarcely broader. The terminal joint 

 of the labial palpus is excessively dilated, but a notch or emargination can scarcely 

 be detected on it. The front coxse are rather broadly separated, and the prosternal 

 process behind then becomes extremely broad, so that it is frequently much broader 

 than long, it is nearly truncate behind, and its angles are either rectangular or 

 acute ; tiie front band of the prosternum is rather large, and does not present any 

 perpendicular face in the middle ; the pectoral prominence is very highly developed, 

 so that there is formed as it were a continuous prominent platform extending along 

 the middle of the body from the front coxse to the hind legs, and becoming broader 

 as it extends backwards ; this prominence is more or less punctate, while the 

 adjacent parts are smooth ; the suture between the metasternum and hind coxa, does 

 not approach very near to the middle coxa ; the coxal processes are highly developed, 

 and greatly prolonged behind, the prolonged angles being rendered acute by a group 

 •of rigid ciUse : the swimming legs are highly developed, the femora and tibiae being- 

 much incrassate and flattened, the former are traversed along the middle of their 

 lower face with a series of punctures parallel with the hind margin, and are 

 furnished at the extremity of their hind margin with an extremely highly develojied 



