106 Journal New York Entomological Society. [Vol. xin. 



Taking up the three species left in group I, verticalis, hybtidus 

 and fasciventris, we can at once separate verticalis by its very large 

 size and a subapical yellow line on the elytra running out as a sort of 

 spur from the marginal band near the apical angle and continuing 

 nearly to the suture. Neither hybridus nor fasciventris has this line. 



To separate the two remaining species is very simple, both male 

 and female having very distinct characters. 



In the males of fasciventris the middle tarsi have the three dilated 

 joints formed into one compact, parallel, spongy cushion, while in 

 hybridus this cushion is distinctly divided longitudinally by a glabrous 

 space. 



In fasciventris the female has the elytra always sulcate while in 

 hybridus they are always, as in the male, smooth. 



There are other distinct and interesting characters by which to 

 separate the various species, but I have tried to bring to notice those 

 most readily observed. 



The division of the dilated joints of the middle tarsi in the male of 

 hybridus by a glabrous space, as mentioned, at once distinguishes it 

 from any other species of Dytiscus. 



We can summarize the distinctive characters as follows : 



D. fasciventris. — Labrum distinctly emarginate ; coxal processes 

 rounded, not produced ; basal and apical thoracic yellow markings 

 absent, or a mere trace ; dilated joints of middle tarsi of male forming 

 one compact, parallel, spongy cushion ; females always sulcate. 



D. hybridus. — Labrum distinctly emarginate; coxal processes 

 rounded ; a fine, linear yellow line at base of thorax and a fairly dis- 

 tinct margin in same color at apex ; dilated joints of middle tarsi in 

 male separated beneath longitudinally by a glabrous space. Females 

 always smooth. 



D. verticalis. — Labium distinctly emarginate ; coxal processes 

 rounded, not produced ; no trace of basal and apical yellow thoracic 

 margins ; a yellow subapical line on the elytra starting from the mar- 

 ginal band and nearly attaining the suture. Females smooth. 



D. marginalis. — Labrum distinctly emarginate ; coxal processes 

 rounded ; thorax with a distinct apical and basal yellow margin, the 

 basal one being broader in its middle portion. Females dimorphic. 



D. dauricus. — Labrum distinctly emarginate ; coxal processes pro- 

 duced, distinctly spinose ; thorax at base, apex and sides broadly 

 bordered with yellow. Females dimorphic. 



