138 COLEOPTERA OF NORTH AMERICA. 



are distinguished from all other groups having the anterior coxa? 

 prominent and the side pieces of the metathorax narrow* by the 

 sixth ventral segment not being visible ; the fifth and propygidium 

 are closely connate, with the suture indistinct, and the spiracle is 

 placed midway between the anterior and posterior margins ; the 

 ventral sutures are distinct in all of our genera, and the apical 

 margin of the thorax is membranous, except in Alobus ; the 

 antennas are 10-jointed, except in Diazus. 



Anterior claws with a slightly prominent tooth near the tip ; middle and 



posterior claws cleft. Oksonyx. 



Claws alike on all the feet ; 

 Last joint of maxillary palpi oval, somewhat pointed; 



Antennae 9-jointed ; claws entire. Diazus. 



Antennae 10-jointed ; claws cleft or toothed. Diplotaxis. 



Last joint of maxillary palpi elongate, cylindrical; claws with a very 



large tooth. Alobus. 



Sub-Tribe 7.— Melolontliini (genuini). 



This is the first of the sub-tribes in which the anterior coxae 

 are not prominent, but simply transverse, and contained entirely 

 in the coxal cavities. It is distinguished from the other sub-tribes 

 having this character, by the labrum being deeply emarginate, and 

 the ventral segments connate, though the sutures are frequently 

 not effaced. 



The apical margin of the thorax is never membranous ; the 

 fifth ventral segment is connate with the propygidium by an angu- 

 lated suture, sometimes partly obliterated ; the spiracle is placed 

 at the angle of this suture, nearer the posterior than the anterior 

 margin. The genera indicate three groups, distinguished as 

 follows : — 



Side pieces of metathorax narrow ; 



Labial palpi on the under surface of the ligula. Rhizotkogi. 



Labial palpi at the sides of the ligula. Tostegopter^. 



Side pieces of metathorax wide. Melolonth^;. 



Group I.— Rhizotrogi. 



This group is sufficiently distinguished by the labial palpi* 

 being inserted on the under surface of the ligula near the sides. 



* For an important note concerning the structure of the ligula and posi- 

 tion of the labial palpi in various groups of Melolonthida?, vide Duval, Gen. 

 Col. Europe, III. 44. 



