On Aquatic Carnivorous Coleoptera or Dytiscidce. 863 



considerable in Hydroporus polonicus (No. 406) ; while in certain species (e.g., 

 Dytiscus ijarallelogrammus (No. 416), Dytiscus imjiressopunctatus (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 segments 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 will 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 coxae. 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 coxte 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 tibise are 

 glabrous externally, possessing only a single series of punctures. 



The four species associated in this aggregate are not by any means closely related 

 hiter se ; and may indeed prove to be incorrectly placed as one genus. The general 

 form is that of Dytiscus inaequalis (Coelambus) or Dytiscus ovatus (Hyphydrus), 

 and the shape of the head and eyes especially suggest such likeness : Chostonectes 

 sharpi is nearest in form to D. insequalis, 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 tibise, a well marked hum.eral 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. 



