OBSERVATIONS. 



This large and splendid species occurred 

 within a hundred miles of the Rocky Moun- 

 tains, on the banks of the Arkansaw river. It 

 was not uncommon, and in consequence of the 

 striking colour of the wings, as well as of its 

 slow and steady flight, it was readily observed 

 and taken. It was occasionally found perched 

 on flowers, in company with Stizus grandis, 

 Nobis, and other Hymenopterus insects. The 

 strongest similarity certainly exists between the 

 P. formosus here represented, and the Pepsis 

 marginata, Beauv., but that species is so much 

 larger, that we cannot believe it to be the same. 



The upper figure of the plate. 



PLATE 42. 



