SCARABiEIDAE. 263 



Group III. — Cremastochili. 



Besides the greater development of the mandibles, and the 

 position of the last spiracle near the posterior extremity of the 

 obliterated suture between the fifth ventral and propygidiura, the 

 inentum in our species affects a very unusual form ; it is, in fact, 

 a large cup-shaped body, sometimes acute behind, sometimes 

 incised, but passing by gradation from one to the other form. 

 The mesosternum is not protuberant. 



The species are elongate, dull black or brown, coarsely punc- 

 tured insects, with the upper surface flattened, and entirely desti- 

 tute of the varied colors which render the species of the two 

 preceding groups so ornamental. Our species all belong to one 

 genus, Cremastochilus; the differences in the form of the mentum 

 are very great. Several synopses have been published. 



True Cremastochilus, having the mentum deeply concave, and 

 incised behind, is confined to the Atlantic slope, as far as the 

 Platte River; the groups with the mentum pointed behind are 

 distributed from the Platte River to the Pacific Ocean. 



Sub-Tribe 2.— Tricliiiiii. 



These insects are readily distinguished by the side pieces of 

 the mesothorax not rising so as to be visible above, and by the 

 elytra not being sinuate on the sides; the thorax is narrower than 

 the elytra, and usually rounded on the sides, giving the insects a 

 different appearance from those of the preceding sub-tribe ; the 

 last spiracle is nearer the anterior than the posterior margin of 

 the segment in Osmoderma, about the middle in Trichius and 

 Gnorimus, and near the posterior margin in Yalgus. 



No species of this sub-tribe has yet been found on the Pacific 

 slope. 



Our four genera may be thus arranged, none having the meso- 

 sternum protuberant: — 



Posterior coxae contiguous ; 



External lobe of maxillre corneous. Osmoderma. 

 External lobe of maxillie coriaceous, lamelliform ; 



Elytra longer than wide, thorax sinuate at base. Gnorimus. 



Elytra not longer than wide, tliorax rounded at base. Trichius. 



Posterior coxae widely S(!parat(rd. Valgus. 



We have strong doubts whether Gnorimus should be retained 

 as distinct from 'J'richius, 



