On Aquatic Carnivorous Coleoptera or Dytiscidw. 599 
I. 57.—Genus AGA BETES. 
Prothorax without lateral margin; upper surface with a dense remarkable 
sculpture. Coxal lines conspicuous, parallel in front, gently divergent behind, and 
marking off a large, broad, coxal border. 
The only species known is found in North America, but is apparently very rare. 
906. Colymbetes acuductus, Harr., Agabus acuductus, M.C.—Ovalis, latus, sub- 
depressus, subopacus vel opacus, rufescens, pectore, abdomine, prothorace elytrisque 
infuscatis, thorace elytrisque versus latera rufescentibus; supra striolis disjunctis, 
brevibus, sat profundis crebre ornatus; prothorace brevi, sine margine laterals, 
angulis posterioribus rotundatis. Long. 7, lat. 45 m.m. 
The male has the basal joints of the front and middle tarsi much incrassate and 
greatly compressed, and furnished beneath with scanty, long hairs, mixed with 
which are other rather short hairs bearing rather large palettes ; the claws of the 
-anterior feet are very elongate, and little curved ; they are also rather thick, the 
front one being somewhat more thickened than the other, but it becomes slender 
near the extremity so as to cause the outline beneath to appear sinuate: the apical 
ventral segment is traversed along the middle for its whole length, with two very 
remarkable perfectly parallel deep grooves. There is also a sexual disparity in the 
sculpture of the upper surface, the female being more dull than the male, and 
having the short impressions on the elytra more densely packed. 
In this species the obliteration of the subserial punctures of the elytra is com- 
plete. 
North America, (Pennsylvania, Canada). 820. 
T. 58.— Genus MATUS. 
Prosternum suleate along the middle. 
Three species are known, two of them Australian, the other North American. 
907. Colymbetes bicarinatus, Say, Matus bicarinatus, M.C.—Oblongo-ovalis, 
minus convexus, nitidus, ferrugineus, fere unicoloratus, elytris vix obscurioribus, 
corpore supra parce subtiliter punctulato; capite minus brevi; thorace ad latera 
marginato, prope marginem late, subobsolete, longitudinaliter impresso ; prosterno 
