﻿MELOLONTHIDiE OF THE UNITED STATES. 265 



separate genus, but the preceding species is intermediate in the last mentioned 

 peculiarity, and the former is altogether a sexual mark. The sixth ventral segment 

 is large, and projecfs^downwards ; it is smooth and flat on its anterior surface, strong- 

 ly punctured and hairy on the posterior surface, which is convex, and nearly hori- 

 zontal ; the line where the two surfaces meet is armed at the middle with two large 

 sharp teeth. 



4. DIPLOTAXES. 



This group established by Kirby, but first defined as a sub-group by Lacordaire, 

 contains species of small size, forming the transition from the groups with transverse 

 not prominent anterior costoe, to those with the coxse conical. The thorax is almost 

 always furnished with an apical membranous margin, a character not known to me 

 in any other group except Dichelonychse, which differ by the chelate ungues. Bur- 

 meister's group of Schizonychse should probably enter here, as they differ only by the 

 greater depth of the emargination of the labrum, and the less breadth of the ligula : 

 the former is indeed not free from variation in our species of Diplotaxis. It has not 

 escaped the attentive eye of Lacordaire that the ventral sutures are distinct in this 

 group, not effaced at the middle as in Khizotrogi ; but he mentions that exceptions in 

 this respect are found in Empecta : as that genus has no apical margin of membrane 

 on the thorax, I am in doubt whether it might not be more naturally placed in 

 Rhizotrogi. 



A character not noted by previous authors, which seems to distinguish this group, 

 is the entire coalescence, without perceptible suture between the 5th ventral segment 

 and the propygidium ; I know of no other group in which this takes place, and taken 

 in conjunction with the small pygidium, the disappearance of the sixth ventral segment, 

 the distinctness of the ventral sutures, and the prominence of the anterior coxae, it 

 would seem to render this as distinctly limited as the other groups here recognized. 



Our genera may be thus distinguished : — 



Ungues antici dente parum prominulo apicali, posteriores fissi - - - Orsonyx Lee. 



Ungues omnes conformes : 



Palpi maxillares articulo ultimo ovali - Diplotaxis Kirby 



Palpi maxillares articulo ultimo elongato, cyliudrico - - - - Alobus Lee. 



Orsonyx Lee. 



Corpus oblongum, paulo convexum, alatum ; clypeus margine reflexo, late rotundatus medio subsinuatus, 

 sutura frontali distincta. Labrum concavum, modice emarginatum ; mandibulse validas prominulae ; maxillae 

 mala exteriore ad apicem bidentata; (palpi desunt). Mentum trapezoideum, ligulae latae connatum, antice 

 se micirculariter depressum ; palpi labiales laterales; antennae breves 10-articulatae, clava parva triphylla. 

 Tborax ad apicem membranula coriacea marginatus, linea marginali nulla. Tibiee anticae tridentatae unical- 

 caratae, posteriores extus bicoronatee, ad apicem paulo incrassatae, posticae intus dense pilosae ; tarsi tibiis vix 

 lon<nores, setosi ; unguiculis anticis dente tenui acuto subapicali parum prominulo armatis, posterioribus fissis, 

 parte inferiore latiore acuto subtruncato vix breviore : propygidium fere omnino tectum; 



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