BY THE REV. T. BLACKBURN. 815 



Prosternum (ut in gen, Eydroo) carina elevata postice spinosa 

 instructum. 



Tarsi postici (nee intermedii) vix remiformes. Maris palpi 

 maxillares fortiter dilatati, feminae gracillimi. 



The insects for which I propose this name have very much the 

 appearance of Hydrobius at the fir&t glance. They seem to be 

 to some extent intermediate between M. Lacordaire's subfamilies 

 Hydrophilides and Hydrohiides, having the continuous sternal 

 keel (free at the apex, which is about level with the hind- 

 most edge of the hind cox^e) of the former, with hind tarsi 

 approaching the latter in structure (being narrower and less 

 distinctly remiform than the intermediate tarsi). The following 

 are the leading characters of the genus : — maxillary palpi of male 

 with the joints (especially the third) dilated, of female very long 

 and slender, their second and 3rd joints nearly equal, the 4th only 

 a little shorter; prothorax in front very strongly bisinuate; antennae 

 very peculiar, 9-jointed, the basal 5 not much different from the 

 same in Hydrophilus ; the 6th joint smooth and shining like the 

 preceding, but forming a kind of saucer on which the 7th joint is 

 laid in such fashion that very little of the 6th joint can be seen 

 from above, and very little of the 7th from beneath ; the 7th 

 joint is almost exactly of the shape of the bone of a chicken known 

 as the " merry-thought •" it (as well as the following two) is 

 opaque and pubescent, and ciliated with long golden hairs ; the 

 8th joint is attached to the apex of the thicker lobe (which lies 

 flat on the saucer-like 6th joint) of the 7th ; it (the 8th) is very 

 short, and very strongly produced in an upward direction so as 

 almost to meet the apex of the thinner lobe of the 7th ; the apical 

 joint is an arched transverse plate, its upper surface the concave 

 one. The hind body is roundly (not, as in Hydrophilus, 

 angularly) convex down the middle line. The mandibles • end in 

 two lobes, the external one much the shorter and longer ; as far as 

 I can see (without dissection) they are not toothed within. 



The carinated prosternum, and claws dentate at their base on 

 all the legs, distinguish this genus from Tro2nsternus ; the latter 

 character distinguishes it from Hydrous and Sternolophus. 



