188 COLEOPTERA OF NORTH AMERICA. 



in front; the sutures are double, not excavated in front, except in 

 Bladus and Notliodes, usually nearly straight; the mesostenmm 

 is not protuberant, sometimes acute in front; the coxal plates are 

 gradually dilated inwards, sometimes toothed at the insertion of 

 the thighs. 



Our genera are: — 



Thorax without luminous vesicles ; 

 Tarsi filiform ; 



Presternum not lobed in front ; 



Prosternal sutures straight ; third joint of antennae small. Bladus. 



Prosternal sutures concave outwards ; third joint of antemi;r eijiial 



to fourth. CEstodes. 



Presternum with a short lobe ; front suddenly deflexed at tip, but not 



margined at the middle ; 



Elytra not striate ; prosternal sutures not excavated. Paranomus. 



Elytra striate ; prosternal sutures excavated in front. Nothodes. 



Presternum with a long lobe ; 



Front convex ; coxal plates scarcely narrower externally. 



Sericosomus. 



Front usually more or less flattened ; coxal plates narrow t'xtenially. 



Ungues simple. Corymbites. 



Ungues with a broad basal tooth. Oxygonus. 



Tarsi with the second and third joints lobed beneath. Asaphes. 



Thorax with luminous vesicles. Pyrophorus. 



The genus Corymbites contains a great number of species, and, 

 as is usual in large genera, is quite polymorphous; some of the 

 species (C selhiops and C. maurn!^) liave the coxal plates almost 

 as suddenly dilated internally as in certain Ludii of the preced- 

 ing sub-tribe. Some of the species are very narrow, resembling 

 Athous and Campylus, others very stout. They may be divided 

 into many groups, which are natural, but not entitled to. rank as 

 genera. 



Group V. — Melanactes. 



This group is represented in our fauna by the genus Melanactes 

 alone, which, while confined to temperate North America, is 

 diffused on both sides of the continent. The species are large 

 shining black insects, found under stones. They are distinguished 

 from other groups having the coxal plates gradually dilated in- 

 wards, by the horizontal protuberant mesosternura, which is not 

 connate, as in Chalcolepidiini, but separated by a distinct suture 

 from the metasternum. The front is depressed at the middle, 



