196 On Aquatic Carnivorous Coleoptera or Di/tiscido:. 



the upper surface, it still often exists to a greater or less extent on the apical portion 

 of the wiug-cases [vide gen. Dytiscus, numerous species) ; and in the case of many 

 species where the sculpture is peculiar, it frequently loses its peculiar character to 

 a greater or less extent on this part and approximates on it more or less to ordinary 

 punctuation. 



The anomalous Amphizoa presents us with the only case among the Dytiscidee 

 where sculpture approaching to what is so usual in the Carabidse exists. In the 

 latter family the elytra very frequently bear each eight or nine rows of punctures 

 or striae or punctate striae, and in Amphizoa something of the same sort is found, 

 but the sculpture in this case is without the regularity and definiteness it possesses 

 in the Carabidae. Elevated costae or ribs on the wing-cases are very rare in the 

 Dytiscidae, but occur in Darwinhydrus in conjunction with a punctate surface. In 

 many Hydroporini the surface bears an extremely fine, short, depressed pubescence, 

 but this is an exception to the condition usually prevalent. 



It is worthy of note that in nearly all the cases in this family where we find a 

 peculiar sculpture present and well developed, we may see in allied species such 

 sculpture present in a more rudimentary manner, and thus, as it were, indicating the 

 steps by which it has been developed : this is well exemplified in the genus Copelatus 

 (for notes on the sculpture of which, see page 201). 



The most remarkable fact in the sculpture of the Dytiscidae is the sexual 

 disparity found in numerous species. This sexual disparity when present is of 

 such varied character that I can here only allude to a few instances. In the first 

 series — Dy tisci Fragmentati — no instances of well marked difference in the sculpture 

 of the sexes have been recorded, but it is possible that the peculiar punctuation 

 observed in certain species of Synch ortus {vide Hydrocanthus asperatus No. 18) 

 may prove to be confined to the female sex ; the differences existing in the sculpture 

 of the prosternal process in the two sexes of some sjiecies of Hydrocanthus is 

 accompanied by a change of form in the part, and is no doubt a phenomenon of a 

 quite different category to the remarkable distinctions in the sculpture of the upper 

 surface found in the Dytisci Complicati. 



In many species of Hydrovatus the distinct punctuation of the female is the same 

 as in the male, but yet the former sex has the surface rendered dull (coriaceous) by 

 a very fine additional sculpture. 



In Hyphydrus we find that the females have the punctuation of the upper sur- 

 face very obsolete in comparison with the males, but, nevertheless, in the former 

 sex there is a development of an excessively fine sculpture which renders the surface 

 quite dull : in this genus we find that certain species have two forms of the female, 

 one of them resembling the male in sculpture while the other is dissimilar in the 

 manner just described ; and this phenomenon of dimorphism in the females continues 

 to be of very frequent occurrence in the Dytisci Complicati. Passing to the group 

 Hydroporini we find that in Coelambus certain species show great differences in the 



