182 COLEOPTERA OF NORTH AMERICA. 



thorax narrow. The mandibles are short, and never extend far 

 beyond the Uibrum; they are usually enmrginate, rarely subacute, 

 but not much prolonged at the apex; in the latter ease, however, 

 the raetasternum is not acute in front, as in the next tribe. 

 Sub-tribes may be defined as follows: — 



Coxal pLates suddenly dilated inwards. Elaterini. 



Coxal plates gradually dilated inwards. Cokymbitini. 



Sub-Tribe 1. — Elaterini (genuini). 



No other character can be given to separate this sub-tribe from 

 the next but the form of the plates of the hind coxae, which are 

 suddenly dilated about the middle, with the outer part much nar- 

 rower than the inner; there is always a strong tooth at the 

 insertion of the thighs; the front is margined anteriorly in all of 

 our groups except the last; the prosternum is always lobed in 

 front; the prosternal sutures are double, except in the first two 

 groups, where they are entirely simple; the mandibles emarginate 

 or toothed at the tip; the tarsi are variable in form, but the claws 

 are never serrate. 



The following groups are represented in our fauna: — 



Margin of the front elevated beliind the labrnm ; 



Prosternal spine truncate behind ; scutellum cordiform. Cakdiopiiori. 

 Prosternal spine acute ; scutellum oval ; 



Prosternum broad, sutures single, convex outwards. Cryptohypki. 

 Prosternum moderate, sutures double, straight or coneave ; 



Third joint of tarsi lobed. " Physoehini. 



Fourth joint of tarsi lobed. Monocrepidii. 



Second and third joints of tarsi with long lobes. Dicrepidii. 



Tarsi not lobed beneath. ' Elateres. 



Margin of the front not elevated. LuDii. 



Group I. — Cardiophori. 



The species are usually small, and convex in form, remarkably 

 distinguished by the- prosternal spine being truncate behind, and 

 fitting like a wedge into the mesosternum; the scutellum is cordi- 

 form; the front is margined, but not concave; the coxal plates 

 are suddenly dilated inwards. 



The genera known to occur in our fauna are separated as 

 follows : — 



