On Aquatic Carnivorous Coleoptera or Dytiscide. 863 
considerable in Hydroporus polonicus (No. 406); while in certain species (¢g., 
Dytiscus parallelogrammus (No. 416), Dytiscus impressopunctatus (No. 409), the 
females are dimorphic, one of the forms, and that the rarer, departing greatly in sculp- 
ture from the males, and ordinary females. The most remarkable of the sexual 
disparities is that where the males have the ventral segments of a black colour, while 
they are yellow in the females (Hydroporus flaviventris, No. 420, and H. pallidulus, 
No. 422). In H. enneagrammus the colour of the ventral sezments in the females 
appears to be variable, sometimes nearly yellow, it is in other individuals quite 
black except at the tip. 
The species are confined to the northern hemisphere, and scarcely exist in its 
tropical zone ; several appear to be fond of .brackish or even salt water, and it is 
probable that when the large fresh-water lakes, and salt lakes of America and 
central Asia are well examined, a considerable increase in the known species of the 
genus wili result. 
I. 36.—Genus CHOSTONECTES. (Vide p. 408.) 
Four species compose this aggregate ; they are insects of broad, more or less 
short outline, convex beneath: the upper surface is pubescent, the undersurface 
bears coarse punctuation specially remarkable on the coxee. The head is rounded 
in front, but not margined ; thorax with its greatest width behind; all the legs are 
rather slender, and the posterior femora are slender, especially in their outer portion; 
the hind cox have only a moderate extension; the outer apices of the coxal 
processes are acute ; the elytra have a very distinct, strongly raised internal ridge, 
but no ligula; the genicular area of the epipleura is abruptly limited externally, 
but not by a raised line, though at first sight such a line appears to exist, owing to 
the abrupt cessation of the coarse punctuation of the epipleura. The hind tibiz are 
glabrous externally, possessing only a single series of punctures. 
The four species associated in this aggregate are not by any means closely related 
inter se; and may indeed prove to be incorrectly placed as one genus. The general 
form is that of Dytiscus imeequalis (Celambus) or Dytiscus ovatus (Hyphydrus), 
and the shape of the head and eyes especially suggest such likeness : Chostonectes 
sharpi is nearest in form to 1). inzequalis, Hydroporus gigas being more similar to 
Hyphydrus. 
The genus is approached by Hydroporus latus of the genus Deronectes in more 
than one point of structure, but these Australian insects have a different form from 
it, a coarse punctuation, glabrous posterior tibize, a well marked humeral area to the 
elytra, and acute external apices to the coxal processes ; moreover the terminal half 
of the epipleura is larger. 
The species are peculiar to Australia and Tasmania. 
