218 HYMENOPTERA. 



honej'-j'ellow costa, and a dusky stigma, edged with honey- 

 yellow. The male ditters a little in having black eoxtie. Mr. 

 Walsh states that the larA-a is a pale grass-green worm, half 

 an inch long, with a black head, which becomes green after 

 the last moult, but with a lateral brown stripe meeting with 

 the opposite one on the top of the head, where it is more or 

 less confluent ; and a central brown-black spot on its face. 

 It appears the last of June and earl}' in July, and a second 

 brood in August. They spin their cocoons on the bushes on 

 wliich they feed, and the fl}- appears in two or three weeks, the 

 sixBcimens reared by him flying on the 26th of August. P. 

 sycoplmnta Walsh is an "inquiline," or guest gall-saw-fly, 

 inhabiting a Cecidomyian gall on a willow. 



The genus Euura comprises scA^eral gall-making species. It 

 differs from the preceding genus in the second, instead of the 

 first, submarginal cell having two recurrent venules. Mr. 

 Walsh has raised E. orbitalis Norton (E. genuiua Walsh) from 

 galls found on Salix humilis. This gall is a bud wliich is 

 found enlarged two or three times its natural size, before it 

 unfolds in spring. The larva is twenty-footed, is from .13 to 

 .19 of an inch long, of a greenish white color, and the 

 head is dusky. It bores out of its gall in autumn, descending 

 an inch into the ground, where it spins a thin, silken, whitish 

 cocoon. The gall of E. saUcis-ovnm Walsh is found on Salix 

 cordata. The female is shining yellow, while the ground color 

 of the male is greenish white. The gall of this species is an 

 oval roundish, sessile, one-chambered, gi-een or broAvnish swell- 

 ing, .30 to .50 of an inch long, placed lengthwise on the side of 

 small twigs. The larva is pale yellowish, and the fly appears 

 in April. The fly is, according to Walsh, " absolutely iindistin- 

 guishable by any reliable character from the guest gall-saw-fly, 

 Euura perturhans Walsh," which inhabits dipterous galls made 

 by Cecidomyian flies on the Avillow and grape (Walsh) . If these 

 two ''species" do not differ from each other, either in the larva 

 or adult state, "by any reliable characters," then one must 

 ([uestion whether the variation in habits is sufficient to separate 

 them as species, and whether E. salicis-ovimi does not, some- 

 times, instead of forming a new gall, lay its eggs in a gall ready- 

 made by a dipterous gall-fl3^ We have seen that Od^'nerus 



