S92 Un Aquatic Carnivorous Coleoptera or Dytiscidoe. 



I. 54.— Genus COPELATUS. {Vide p. 562.) 



This is an extensive aggregate, comprising more than ninety species ; they are 

 rather flat insects with a very continuous outline ; and are oval or oblong-oval in 

 form ; the colour is variable, frequently unicolorous black, while not unfrequently 

 there is a 3'^ellow basal band on, and a pale extremity to, the wing-cases ; the size 

 is frequently quite small and the greatest length attained is lu m.m. of length : the 

 sculptu]-e of the upper surface is remarkable and usually consists of regular lines, 

 which frequently form elongate stria? on the wing-cases, but sometimes are abbreviate 

 and broken up, and sometimes are quite wanting ; the upper surface of the laro- 

 thorax frequently bears short irregular scratches. The coxal lines are peculiar, 

 being extremely close to one another, so that near their divergence at the coxal 

 lobes they are almost contiguous with the longitudinal line dividing the two coxae ; 

 moreover at the anterior part of the coxal lobes they become excessively fine, so 

 that they can with difficulty be detected, and are abruptly turned outwards at right 

 angles to their former direction. These peculiarities of the coxal lines are quite 

 sufficient to characterize the aggi-egate ; but it must be added that the sides of the 

 thorax have a veiy fine margin, the prosternal process is never very elongate and 

 the intercoxal process of the metasternum has its anterior part reflexed and im- 

 pressed in adaptation to the apex of the prosternal process, but does not possess 

 any prolonged groove, or highly developed depression in front. The hind coxae 

 are always large, and the wing of the metasternum terminates as a slender band 

 deflexed outside of the front border of the hind coxa. The swimminsf legfs are 

 slender, more especially the tibiae and tarsi, for even in the species where the femora 

 are distinctly incrassate, the tibise and tarsi are scarcely correspondingly developed. 

 The coxal lobes always display a well marked coxal incision and the apex of the 

 posterior femur is destitute of accumulated setae. The hind tarsi are almost, or 

 quite, destitute of lobing of the joints externally, and are terminated by two small, 

 equal, (?laws. The male tarsi are sometimes scarcely different from those of the 

 female (Colymbetes parvulus, Boisd.), in other cases the three basal joints become 

 considerably dilated, and furnished beneath with four rows of distinct palettes, 

 placed almost immediately on the tarsus; their claws are not subject to much 

 elongation or development. The females often show a highly developed sexual 

 sculpture, which seems to be either variable or polymorphic within the limits of 

 one species : this sexual sculpture is independent of the peculiar .sculpture already 

 alluded to, which however is also to some extent liable to sexual differences. 



The genus is wanting in cold climates, but is widely distributed in the warmer 

 parts of the world, and will probably prove to be one of the most extensive in the 

 Dytiscidae. A large proportion of the one hundred species known to me are at 

 present very rare in collections, and it has for this reason been impassible for rae 



