168 ENTOMOLOGICAL SOCIETY 



52^, 45, 37 1 A; (5) 22^, 25, 22^, 22^; (6) 22^, 25, 22^, 20; (7) 35, 

 H, 35, 30. 



A NEW BRACONID OF THE GENUS ELASMOSOMA. 



BY T. D. A. COCKERELL. 



On the afternoon of July 16, 1908, at Boulder, Colo., my 

 wife called me to see a great battle between the ants Formica 

 sanguined Latr. and F. snbpolita Mayr. which was taking 

 place on the pavement adjacent to the university campus. As 

 we watched the conflict, my wife noticed certain minute insects 

 hovering over the ants. They remained hovering in the air 

 about an inch above the ground, darting downwards at inter- 

 vals to alight for an instant on the back of a worker F. sub- 

 polita. Two specimens were collected, and, as was expected, 

 they proved to belong to the curious genus Elasmosoma* 



Elasmosoma vigilans, n. sp. 



Female. Length, 2 mm. or slightly more ; black with a dullish surface, 

 the abdomen more shining ; abdomen a little shorter than thorax ; wings 

 hyaline, the costa and stigma dark brown; legs very pale reddish, the 

 tarsi white, black at apex; antennae dark, 12-jointed, the flagellar joints 

 with numerous longitudinal keels, and with many short pale hairs ; broad 

 apical margin of clypeus, labrum, and mandibles very pale yellowish, 

 the apices of the mandibles ferruginous ; mandibles strongly bidentate, 

 the inner tooth about half as long as the outer; face and front 

 with fine transverse lineolation, passing into reticulation; mesothorax 

 with very fine punctures of two sizes, and scattered short pale hairs ; 

 scutellum similarly sculptured; sides of metathorax with coarse irreg- 

 ular reticulation; abdomen with very fine and very dense punctures, 

 its lateral margin sharp; basal part of marginal neurone brown and 

 distinct, but it ends before level of end of stigma in a swelling, and 

 beyond that is merely indicated by a faint shade. The middle and 

 hind coxae are pale, concolorous with their trochanters and femora. 



The short abdomen alone will readily separate this from E. schivarzi 

 Ashm. and E. pergandei Ashm. ; from E. bakcri Ashm. (from Fort 

 Collins, Colorado) the color of the middle and hind coxae would serve 

 as a mark of distinction, but as E. bakcri is only known in the male, it 

 occurred to me that the present insect might be its female. Mr. J. C. 

 Crawford has very kindly compared one of my specimens (now in the 

 U. S. National Museum) with the type of E. bakcri, and is of the 

 opinion that it is distinct. In E. bakcri the region in front of the 



a Discussed by Ashmead in Proc. Ent. Soc. Wash., in, p. 280. 



