On Aquatic Carnivorous Coleoptera or DytiscidcB. 873 



scutellum is quite exposed, and visible at the base of the elytra, the base of the 

 pro thorax being but little prolonged and not at all acuminate in the middle. The 

 front and middle tarsi are conspicuously five-jointed, the three basal joints being 

 moderately broad (subject however to sexual difference in this respect), the third 

 being emarginate at the apex but scarcely bilobed ; the fourth joint although 

 perfectly distinct is much smaller than the others, and the fifth is rather elongate. 

 The presternum is subvertical in direction between the coxae, and is not in the least 

 thickened, or raised, along the middle ; its process is large, conspicuously margined, 

 pointed at the extremity, which is received into a deep fossa on the apex of the 

 inter-coxal process of the metasternum. The central fork of the mesosternum is 

 imperfectly connected with the metasternum. The hind coxae are of moderate size, 

 about as elongate along the mesial line as near the side, but their front border is 

 a good deal extended in the anterior direction. The hind ooxal cavities are nearly- 

 but not quite contiguous, and the coxal processes form divergent lobes, which have 

 however but little extension in the longitudinal direction. The swimming legs. 

 are quite slender, their tibioe and tarsi being slender and elongate, the latter 

 terminated by two equal curved claws. The wing-cases are acuminate at the 

 extremity, and the body terminates in a projecting mucro. 



These insects have the presternum of the Hydroporini, but no Hydroporini show 

 a conspicuous scutellum, and very few have distinctly five-jointed front and middle 

 tarsi. Thus the aggregate formed by these few species, though it may be classed 

 in the tribe Hydroporides, cannot be placed in any of the groups forming the tribe, 

 and so must remain an isolated genus, f hese insects are so rare, that I have not 

 been able to obtain any specimen for dissection. 



I cannot suggest any valid approximation to other insects, but there may be a. 

 slight approach to the North American Hydroporus oblitus, Aube, and Hydroporus. 

 collaris, Lee, for these insects have the apex of the scutellum distinctly exposed, 

 and the prosternal process and hind coxal cavities are not very dissimilar to what 

 we find in Celina. 



The species of Celina are found only in Southern and Central America, with twa 

 rare species in the United States of North America. 



I. 43.— Genus AIETHLES. {Vide]). 489.) 



This isolated genus at present consists of three species, they are small Hydro- 

 poroid insects, but with the apex of the elytra, and extremity of the body spinose 

 and acuminate. 



The scutellum is quite concealed, the base of the thorax distinctly accuminate in 

 the middle : front and middle tarsi five-jointed, cylindric, the basal four joints sub- 

 equal, without clothing beneath. Prosternum between the front coxae very small, 

 forming a very slender depressed band placed only at a very obtuse angle from the 



