AMERICAN COLEOPTERA. 51 



A. Middle lobe of front with an apical elevated margin, extending to the side 



lobes : 

 Middle lobe rounded, uniformly margined : 



6 mm. Thorax densely punctured 1. opacus. 



fi mm. Thorax and elytra more sparsely punctured 2. musculus. 



8 mm. Middle lobe broadly truncate ?>. simplex. 



» mm. Middle lobe rounded, projecting each side into a small 



erect tubercle ; (elytral strise deep) 4. biarmatus. 



B. Middle lobe of front scarcely, or not at all' margined ; (elvtral strise deeii, 



strongly punctured) : 



7 mm. Head with three apical tubercles and a posterior trans- 



verse ridge 5. complex. 



5 mm. Head with a small acute tubercle on tlie vertex 6. sparsus. 



7*5 mm. Head with an acute frontal tubercle, and a trans- 

 verse ridge on the vertex 7. frontalis. 



6 mm. Head with two transverse ridges 8. duplex. 



Middle lobe slightly truncate, without apical tubercles. 



7 mm. Head with a small posterior transverse ridge 9. striatus. 



7'5 mm. Head without ridges , 10. pectoralis. 



In npacua, muscidns aud simplex the striae of the elytra are very .sliglit- 

 ly impressed, their punctures in opacus and musculus are much larger 

 than those of the intervals, which are arranged in triple series : in shn- 

 plt'.c the punctures of the stride are scarcely larger than those of the 

 intervals, which are closer and less regular than in the other two. 



In biarmatus the margin of the front is curved, but more thickened 

 than in the preceding, so that the front appears concave, and at the jun<- 

 tion of the middle with the lateral lobes, there is on each side a small 

 erect tubercle ; the striae of the elytra are deep, strongly punctured 

 and the punctures of the intervals irregular. 



In complex and sparsus the punctures of the head and the intervals 

 of the elytra are much more distant than in the other species, though 

 more so in sparsus than in complex. 



0. striatus and pectoralis agree in size aud sculpture, but diflPer in 

 the form of the head between the back part of the eyes ; in striatus 

 (Arizona, collected by Dr. Webb), there is a very well defined trans- 

 verse ridge, while in the New Mexican pectoralis there is merely a very 

 gentle swelling, slightly impressed at the middle, forming two faint tu- 

 bercles. The prosternum is longitudinally very prominent in the spe- 

 cies last named, but not in any of the others. 



0. opacus and musculus agree in the form of the front and general 

 sculpture, except that the thorax of the former is more densely granu- 

 lated, and the punctures of the intervals of the elytra are more nu- 

 merous aud less regularly arranged in triple series. 



The hind femora in musculus are armed at the tip with a large acute 



