IT 2 COLEOPTERA OF NORTH AMERICA. 



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

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

 species (C. sethiops and G. maurus) have the coxal plates almost 

 as suddenly dilated internally as in Crigmus, of the group Ludii 

 of the pi'eceding 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 dif- 

 fused 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 mesosternum, which is not 

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

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

 and not margined ; the mandibles are toothed near the tip ; the 

 prosternum is furnished with a long lobe in front; the sutures 

 are double, nearly straight, slightly excavated in front ; the coxal 

 plates are gradually dilated inwards and toothed at the origin of 

 the thighs ; the tarsi are not lobed, but very densely pubescent 

 beneath, with the joints 1 — 4 gradually decreasing in length; the 

 claws are simple. 



Tribe V.— PLASTOCERINI. 



In this tribe I comprise certain genera which recede from the 

 true Elaters to approach the Cebrionida? ; thus, the sixth ventral 

 segment is usually slightly visible, and in the female of Euthysa- 

 nius becomes equal to the other segments. The same insect is 

 further remarkable for the elytra being very short, and the wings 

 wanting; in the female of Plastocerus the elytra are somewhat 

 dehiscent, but the wings are present. 



The following characters distinguish this tribe : The mandibles 

 are curved and slender at the tip, and project more than in other 

 Elaterida? ; the labrum is more closely connected with the front ; 

 the prosternum is truncate in front, not at all lobed, and its late- 

 ral sutures are straight, slightly oblique, not excavated in front ; 



