On Aquatic Carnivorous Coleoptera or Dytiscide. 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 ciliz are not included, 
the breadth given being that of the joints themselves ; if the marginal ciliz 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. Aubé 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. \ SPENCERHYDRUS. 
Three Australian species. (Vide below.) 
HOM@ODYTES. 
(Vide p. 703.) 
{ Coxal lines absent ; unguicular cleft broad at base. 
| Three Australian and New Zealand species. 
MEGADYTES. 
(Vide p. 704.) 
Anterior border of hind foot in the male sex. Six- 
coxa rather widely 
separated from the 
middle coxa. 
teen South American 
Coxal lines present ; : 
1 P i species. 
unguicular cleft 
narrow and an- 
| gular at the base. 
Only one claw on hind foot 
in the male sex. Fifty 
| species ; none from South 
[ | America. 
CYBISTER. 
{ Two distinct claws on : 
f (Vide p. 714.) 
J 
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 
eanaliculate 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 No. 1097 
raised ; side of wing-case moderately broadly yellow. ; 
Prothorax evenly convex ; side of wing-case very broadly yellow. j Nos. 1098 and 1099, 
1097. Spencerhydrus pulchellus, n. sp.—Parvus, oblongo-ovalis, sat convexus, 
supra olivaceus, capite anterius prothoraceque ad latera testaceis, elytris vitta 
marginali lata, sed ad apicem evanescente, testacea ; subtus piceus, pedibus quatuor 
4X2 
