On Aquatic Carnivorous Coleoptera or Dytiscidce. 199 



sively minute interstitial sculpture, having a somewhat granular appearance. 

 Passing to the Dytiscini we meet in that group with some most remarkable facts : 

 in the genus Hyderodes the females are usually smooth and polished like the males, 

 but they are dimorphic, inasmuch as a second form of the female is met with 

 (apparently only rarely) in which the surface is excessively rough, the whole of the 

 upper surface, except the head, being covered with deep coarse erosions or corru- 

 gations, irregular in shape and direction. In the genus Dytiscus considerable dis- 

 crepancies exist among the various species in the sexual sculpture ; in D. 

 punctulatus the female has ten grooves on the basal portion of the wing-cases, and 

 the whole of the rest of the upper surface, including the interstices of these grooves 

 bears a close fine punctuation, while in the male the grooves are wanting, and the 

 elytra are punctured only on the apical portions ; the female in this species has also 

 even the undersurface rendered dull over a considerable portion of its area by the 

 •existence of fine, short scratches or reticulations which are not found in the 

 other sex ; in D. fasciventris the facts are similar except that the fine sculpture is 

 less extensively developed, so that as regards this latter peculiarity the sexes are 

 more alike than they are in D. punctulatus. In Dytiscus habilis, in D. hybridus, 

 and in D. verticalis the females have no grooves on the wing-cases, but they differ 

 from the males by a greater development of the punctuation on the apical portion 

 of these parts, and also by possessing an additional fine punctuation on the lateral 

 basal portion of the wing-case ; in D. verticalis this additional punctuation is very 

 small and unimportant ; the females of these three species all possess too a con- 

 spicuous special sculpture on each side of the prothorax ; in D. subllmbatus 

 the female characters are approximately the same as in D. punctulatus and 

 fasciventris, but in this species there also exist females differing in sculpture from 

 the males only by their possessing a fine scanty punctuation on the lateral portions of 

 the prothorax ; a similar condition is present in Dytiscus marginalis, the females 

 differing greatly from the males by their grooved and much punctate surface, but 

 individuals of their sex are found differhig from the males only by a slight punc- 

 tuation on the thorax and a little greater development of that on the elytra. In 

 D. circumcinctus we again find the females possessed of a grooved and much 

 punctate surface, but here a second form of the female occurs quite without sexual 

 punctuation or grooving of the wing-cases. The females in the genus Dytiscus 

 differ then from the males by possession of a fine sexual sculpture, and by a groov- 

 ing of the elytra, this latter feature is however not found in certain species, and in 

 certain other species is sometimes present, sometimes absent, while the fine sexual 

 sculpture of the females is more constant, but may also be occasionally quite absent, 

 and is only present in its greatest development in such females as are sulcate. In 

 the Hydaticides, we find certain species of Acilius possessing females with grooved 

 wing-cases, but the grooves are very different from what exists in Dytiscus, they 

 being but four (instead of nine or ten) in number, and furnished with a pubescence 



