230 MESSKS. T. BLACKBURN AND P. CAMERON ON THE 



in the brilliancy of the silvery pilosity on the clypeus_, and 

 in other points. Its eyes are considerably more strongly 

 facetted. The punctuation differs slightly; on the naeso- 

 thorax it appears a trifle more sparing and rugose, while 

 the metatborax is smoother and more evenly punctured. 



42. Crabro unicolor. 



Crabro unicolor, Smith, Cat. of Hymen. Ins. iv. p. 421. 

 I have not seen the original description of this insect ; 

 my own examples were named by Mr. Smith. As com- 

 pared with other Hawaiian species, the eyes appear to be 

 sepaiated by about the usual space (or even a little more) 

 and to be facetted ratber coarsely. The shape of the hind 

 body is similar to that of C. mandibularis , being evidently 

 longer and narrower than in C. affinis and C. stygius and 

 their allies. The bright steely-blue colour of the wings is 

 a conspicuous character. In the male the sixth joint of 

 the antennae is distinctly but not strongly dentate, and the 

 flattened or concave space on the ventral segments begins 

 near the apex of the third segment. 



I have met with this insect on Oahu and Maui. It 

 appears to be the commonest of the Hawaiian Crabronidse, 

 probably occurring on all the islands. 



43. Crabro stygius. 



Crabro stygius, Kirbj, Eut. Month. Mag. xvii. p. 88. 



The extremely wide separation of the eyes (between 

 which the forehead is scarcely concave), which is exagge- 

 rated to the utmost in the female, is the striking feature 

 of this and the following two species. The eyes are rather 

 finely facetted, the hind body resembles in shape that of 

 C affinis, Smith, and in the male the sixth joint of the 

 antennae is feebly dentate. In this sex the character of 

 the ventral segments is rather peculiar, consisting of a 



