AMERICAN COLEOPTERA. 383 



Revision of the DYTISCIDJE of the United States. 



BY G. R. CROTCH, M. A., CANTAB. 



This family is one of considerable interest, from the very wide dis- 

 tribution of some of its species. Several American species are here 

 considered identical with their European forms, and probably further 

 comparisons will show that the number common to the two countries 

 may be increased. 



The difficulty of determining the species is very great in some of 

 the genera, and only large series of specimens can resolve it. The 

 peculiar dimorphous females occur here as in Europe, only in Dytiscus 

 proper, nearly all are permanently smooth in the 9 , while in England 

 all except one are permanently sulcate. In other genera as Agabus 

 and Acilius the smooth and rough females are equally common. The 

 number of genera has been considerably increased, but I am unable 

 to group them into larger divisions with any exactitude. Particular 

 attention has been paid throughout to the form of the metasternum 

 and the coxal appendages, characters neglected by all except C. G. 

 Thomson. 



The annectant families AmpMzoidse and Pseudomorphidze lead me 

 to suppose that this family ought not to be separated from Carabidae, 

 but that the first three divisions should form one natural family, dis- 

 tinguished by the antennae, palpi, and first ventral segment. 



Two very distinct sub-families are indicated : 



Coxal plates very large, covering the ventral segments HALIPLIDES. 



Coxal plates large, connate with the metasternum DYTISCIDES. 



Haliplides. 



A. Thorax quadrate with lateral impressed line Brychins. 



Ab. Thorax narrowed in front. 



B. Interstices of the elytra punctate Haliplus. 



Bb. Interstices impunctate Cneniidotus. 



BRYCHIUS, Thorns. (Type elevatus.) 

 B. llornii. sp. n. — Pale yellow, head and thorax obsoletely punctate; ely- 

 tra striate punctate, interstices smooth, the punctures form narrow black lines, 

 and towards the margin are three clouded black spots; beneath ochreous, 

 metasternum punctate. L. *14 inch. 

 California. (Horn.) 



