444 TERTIARY INSECTS OF NORTH AMERICA. 



the body. The thorax is generally only twice as broad as the median length, 

 but sometimes considerably more than that, tapering in a very variable 

 degree, sometimes rapidly and regularly, but always with a rounded curve, 

 sometimes so slowly as to leave the lateral angles of the front very prom- 

 inent, and making the thorax here twice as wide as the head ; the basal 

 margin is truncate. Scutellum rather large and especially broad, triangular, 

 with straight sides, always shorter than broad, and yet generally reaching 

 nearly half-way to the tip of the abdomen. 



A large number of species are known, as many as in the preceding 

 genus, all but one, which comes from Green River only, being found at 

 Florissant, one of them very abundantly. 



Tuhle of the species of Necrocydnua. 



Body more than half as long again as broad. 



Thorax considerably more than twice as broad as the median length. 



Body relatively slender ; thorax tapering considerably, the breadth at the bottom of the apical 



emargination about three-fourths that of the basal margin 1. Jf. tuleanius. 



Body relatively stout; thorax tapering but little, the breadth, as above, about seven-eights 



that of the basal margin 2. N. gosiutenais. 



Thorax only twice as broad as the median length. 



Thorax tapering considerably, the lateral angles of front not prominent. 

 Head broad, nearly or quite a third as broad as base of thorax. 



Smaller species ; emargination of apical border of thorax deep, half as long as greatest 



breadth of thorax 3. N. torpens. 



Larger^ species ; emargination of apical border of thorax shallow, considerably less 



than half as long as greatest breadth of thorax 4. N. stygius. 



Head relatively narrow, hardly more than a fourth the breadth of the base of the thorax. 



5. N. amijzonus. 

 Thorax tapering but little, the lateral augles of front prominent. 



Smaller species, hardly exceeding four millimeters in length, less than two-thirds as long 



again as broad; abdomen full and rounded 6. N. senior. 



Larger species, more than five millimeters long, and about three-fourths as long again as 



broad; abdomen tapering 7. N. solidalus. 



Body less than half as long again as broad 8. N. rerectux. 



1. NECROCYDNUS VULCANIUS. 



Head rounded triangular, broader than long, with the large eyes nearly 

 half as broad as the base of the thorax. Thorax considerably more than 

 twice as broad as the median length, subtrapezoidal, the sides tapering so 

 that the breadth near the front (at the bottom of the apical emargination) is 

 about three-fourths that of the basal margin, the lateral angles rounded 

 somewhat, the apical emargination half as broad as the thorax, and a third 

 as deep as broad, very regular, the surface uneven from the elevation of the 

 sides in front to irregular bosses, and rather coarsely, faintly, and sparsely 

 punctate. Scutellum small, not more than half as long as broad, regularly 



