On Aquatic Carnivorous Coleoptera or DytiscidcB. 



701 



and keep it flat ; when this has been done the specimen should be left to dry, and 

 the tarsus will afterwards remain extended and flat, so that its dimensions and 

 structure can be readily ascertained. 



In the measurements I have given of the tarsi, the marginal cilise are not included, 

 the breadth given being that of the joints themselves ; if the marginal cilise are 

 included (when the tarsi have been flattened out) it will be found that the dimen- 

 sions are considerably greater than those I have recorded. The structure of the 

 cedeagus offers very important differences in this genus, and some species are more 

 readily distinguished by examining it than by any other means. Aube and others 

 have attached much importance to the presence or absence of a reddish spot near 

 the extremity of the wing-case ; but this seems to be an eminently variable cha- 

 racter, so that much attention need not be given to it. 



The group comprises four genera, which may be tabulated as follows : — 



Anterior border of hind coxa approaching rather closely to the middle coxa. ) S- 

 Three Australian species. J 



Anterior border of hind 

 coxa rather widely 

 separated from the 

 middle coxa. 



Coxal lines absent ; nnguicular cleft broad at base. 

 Three Australian and New Zealand species. 



Coxal lines present ; 

 unguicular cleft 

 narrow and an- 

 gular at the base. 



Two distinct claws on hind 

 foot in the male sex. Six- 

 teen South American 

 species. 



Only one claw on hind foot 

 in the male sex. Fifty 

 species ; none from South 

 America. 



SPENCERIITDRUS. 

 ( Vide below.) 



IIOMCEODYTES. 

 (Vide p. 703.) 



MEGABYTES. 

 {Yide^. 704.) 



CY BISTER. 

 {Yide\>. 714.) 



I. 76.— Genus SPENCERHYDRUS. 



Anterior border of hind coxa approaching closely to the middle coxa, terminal 

 portion of wing of metasternum moderately abruptly deflexed. Prosternum deeply 

 canaliculate along the middle. Side of wing-case broadly yellow. Australian 

 species. 



This genus comprises two very distinct forms : — 



Prothorax depressed close to the side, so that the margin appears to be 1 

 raised ; side of wing-case moderately broadly yellow. j 



Prothorax evenly convex ; side of wing-case very broadly yellow. 



No. 1097. 



i 



Nos. 1098 and 1099. 



1097. Spencerhydrus pulchellus, n. sp. — Parvus, oblongo-ovalis, sat convexus, 

 supra olivaceus, capite anterius prothoraceque ad latera testaceis, elytris vitta 

 inarginali lata, sed ad apicem evanescente, testacea ; subtus piceus, pedibus quatuor 



4X2 



