154 LENG AND HAMILTON. 



Thorax with four callosities ; pygidiiini of 9 stroujjly protuberant. scliaillllii. 

 Thorax with two callosities ; pygidium of 9 feebly protuberant. 



Elytra truncate at tip tripnnctata. 



Elytra rounded at tip ocellatu. 



Thorax without callosities; pygidiuni of 9 feebly protuberant. 



Elytra not pubescent gracilis. 



Elytra closely clothed with recumbent pubescence ruficollis. 



O. schaiiiuii Lee. 1852, Jour. Ac. Phil. ser. 2, ii, p. 153 ; wapleri Chev., Eev. 

 Zool. 1852, p. 420 ; qundricallosa Lee, 1874, Trans. Am. Ent. Soc. v. p. 68. 

 Length 11-15 mm.; .45-60 inch. Habitat. — United States and Canada. 



The color varies greatly. In the palest form the entire insect is 

 flavo-testaceous, except the feet and basal joints of antennae. In the 

 darkest form, the abdomen, femora, tibiae and thorax are pale, while 

 the rest of the body, including the thoracic callosities, are nearly 

 black. In the intermediate forms the black color may be traced 

 through different individuals, in a series of which the palest and the 

 darkest forms are simply the extremes. It seems useless, therefore, 

 to tabulate individuals which mimic races and varieties only in 

 meagre collections. Breeds in the living twigs of cotton wood 

 {Populiis moiiUifera), Riley. 



O. TRiPUNCTATA Swcd. — Under this name are included a great 

 many specimen;^. They may be readily separated into two varieties: 



Body beneath black var. biiiiaeiilata. 



Body beneath in great part yellow var. tripiiiictala. 



That the individuals, which can easily be separated by the color 

 of the body beneath, constitute varieties of one species seems to me 

 certain. The black abdomen in the first is usually accompanied by 

 black legs and entirely black elytra, the yellow abdomen of the 

 second by yellow legs, yellowish antennje, and more or less sti'iped 

 elytra. Yet every large collection will contain specimens of var. 

 hivmcnkda in which the legs are at least brownish and the elytra 

 decidedly vellow through the miildle, wherelTy the black abdomen 

 alone remains to differentiate the varieties. The color of the legs 

 very rarely becomes (juite pale, even in the var. bimaculata, and 

 such an individual received the mime flavipes from Haldeman. Other 

 variations also occur in the maculation of the thorax, etc., and the 

 following table will serve to separate the most striking. Individuals 

 occur frequently which will not answer to any of the names. 



