848 On Aquatic Carnivorous Coleojitera or Dytiscidoe. 



and Carabidte are themselves distinct families, and that as its departures from the 

 Carabidse are in the Dytiscidas direction it may be placed with the latter. It is a 

 creature which may be considered to have retained a more primitive condition in 

 certain portions of the organization, (antennge, maxillary lobe, and legs, coxse excepted) 

 than have other members of the Dytiscidse or Carabidje, while its hind coxai and 

 thoracic segments have been the subjects of an evolution similar to that of the same 

 parts in Dytiscida). It is Dytiscid inasmuch as it lives in water, it is Carabid inas- 

 much as it moves on a solid surface in that water ; now as there are no Carabidse 

 having the middle coxal cavities formed as they arc in Amphizoa and as in this 

 respect it agrees with the majority of Dytiscidse, these reasons entitle us to place 

 it with the latter in a natural classification. 



Note. — I consider that the punctate antennge of Amphizoa may be justly considered 

 a more primitive condition of those organs than the pubescent antennae of '^'arabidse 

 or the glabrous antennae of Dytiscidae, for the following reasons; the antenna} of 

 Carabidse are complex organs of sensation, perfection being obtained by means of 

 punctuation (?), setae, and delicate pubescence,* the simply punctate antennae of 

 Amphizoa are therefore clearly more primitive than the punctate-setose-pubescent 

 antennae of Carabidae. As regards the comparative primitiveness of the glabrous 

 antennae of Dytiscidae and the punctate antenna? of Amphizoa, the facts are not so 

 clear, and it would at first appear that the glabrous antennae of Dytiscidae should be 

 treated as more primitive than the punctate Amphizoa antennae; but there is reason 

 to believe that the antennae of Dytiscidae have been more or less punctate before 

 becoming glabrous ; thus in Pelobius (the most imperfect Dytiscid or Carabo- 

 Dytiscid), the basal joint of the antennae is a good deal punctured, in Scutopterus 

 (S. horni, Crotch) a higher form, a slight punctuation of the basal joint exists, and 

 traces of such punctuation may be perceived even in Dytiscus, while in the highest 

 Dytiscidai (Cybister for example) the antennae are completely polished and free from 

 punctuation. In writing of these insects I consider therefore I am entitled to treat 

 antennae with a punctuation on the basal joints as more primitive than polished, or 

 highly pubescent, antennaj. 



I. 17.— Genus HYDROVATUS. {Vide p. 321.) 



This aggregate is formed by the union of about forty .species. The individuals 

 are of small size, and of broad, convex, short, sometimes quite rotund form ; the 

 elytra are more or less acuminate behind, and there is frequently a small spine 

 pi'ojecting from the termination of the body ; the swimming legs are very slender 

 and little developed. The clypeus is large, and overhangs the labrum ; this, how- 

 ever, is seen to be exserted and visible when the undersurface of the head is 



* I say this without conaidei'ing at all what relation this punctuation may bear to the pits described by 

 Erichson and others as forming part of the sensitive apparatus of the antenniB of the Coleoptera. 



