91G On Aquatic Carnivorous Coleoptera or Dytiscidce. 



I. 76.— Genus SPENCERHYDRUS. {Vide p. 701.) 

 Three species form this aggregate ; they are amongst the smallest of the 

 Cybistrini, scarcely attaining 20 m.m. of length ; the yellow colour on the lateral 

 part of the wing-case is extensive. The upper border of the hind coxae is greatly 

 approximate to the middle coxal cavities, the laciniae of the metasternum being 

 shorter and more linear, and less abruptly turned backwards than is the case in 

 Cybister : the coxal lines are present ; the prosternum is channelled along the 

 middle ; the hind tarsi bear two claws of which the inner is much the laro-er, the 

 unguicular cleft is broad and short, its anterior part curved, not angular : the 

 palettes of the male tarsi are subelliptical, and without paper-like external prolon- 

 gations. 



The three species agreeing in the above characters may be arranged in two 

 groups according to whether the side ot the thorax appears to be raised (S. 

 pulchellus), or is normal and without &nx appearance of being margined (S. 

 latecinctus, and S. semiflavus). They depart from all the other Cybistrini by the 

 male tarsi, the fifth joint of which is unusually elongate, while the palettes on the 

 undersurface of the dilated basal joints are of peculiar form being destitute of the 

 external paper-like prolongations found in all the other aggregates. The genus 

 agrees with Homoeodytes in the structure of the hind claws, and the form of the 

 unguicular cleft, but departs from it by the presence of coxal lines, as well as by 

 the form of the lacinise of the metasternum, and the peculiar male tarsi. 

 The three species are peculiar to Australia, and very rare in collections. 



l.'JI.—QeuMsHOMCEODYTES. (Hc/ep. 703.) 

 Three species form this aggregate. The individuals are of the usual Cybister 

 form, Avith lateral stripe on the elytra. The size varies from 15 to 27 m.m. of 

 length. The coxal lines are completely absent, and by this character they depart 

 from all the other Cybistrini ; the structure of the hind claws and their point of 

 insertion is much the same as in Spencerhydrus ; they differ therefore from 

 Megadytes and Cybister in this respect, but the structures of the male tarsi and 

 of the lacinise of the metasternum agree with the two genera just mentioned. 



The three species are sufficiently discrepant to form two well marked groups ; 

 A, (Dytiscus atratus) size small (15 m.m. long) prosternal process distinctly chan- 

 nelled along the middle ; postero-external angle of hind femora rectangular; 

 intermediate male tarsi with largely developed sexual pubescence on the three 

 basal joints, female without sexual sculpture ; and B, (C. scutellaris, and C. hookeri), 

 size moderate (about 25 m.m. long), prosternal process with channel obsolete ; 

 postero-external angle of hind femora acute or spinose ; male tarsi with sexual pubes- 

 cence on the third joint but not on the two basal joints, female with very dense fine 

 sexual sculpture on the wing-cases. 



The species are found in Australia and New Zealand, 



