84 ANDRIOUS RADICIS. 



The form of the gall is very irregular ; it may be 

 pear-shaped, round, or oval; and on the trunk espe- 

 cially it may take the form of a mere swelling. As has 

 already been pointed out (p. 2), it seems very possible 

 that more than one individual may unite to form such 

 large galls as those mentioned above. 



The only inquiline is Synergus incrassatus, Htg. 

 Of parasites there are Torymus nobilis, T. erucarum 

 (Gynipidis, Wlk.), T. amoenus, T. radicis, Gir. (Giraud); 

 Pteromalus quercinus, Gir. (Giraud) ; Tetrastichus 

 quercus, Wlk. (Giraud) ; Eurytoma rosse. 



The first development of the gall takes place in 

 September ; but the growth which then takes place is 

 very slight, and stops during the winter, until, with 

 the spring and the renewed life of the tree engendered 

 by the heat, the gall recommences growth and soon 

 reaches its full development. 



I have found the flies out as early as February, and 

 alive in the galls in December ; but these examples 

 were, no doubt, specimens whose development had 

 taken a year longer. 



Sexual Form. — Brownish-red ; the head and thorax marked with 

 black, or for the greater part black ; abdomen also more or less black : 

 the legs pale testaceous ; wings hyaline. Head dilated behind the 

 eyes. Vertex and mesonotum finely shagreened; scutellum finely 

 rugose. 



The <$ is moi'e shining, and has the head and thorax black, the legs 

 of a clearer obscure yellow, the hinder femora and tibiae often infus- 

 cated ; the antennae testaceous at the base, the rest more or less infus- 

 cated. 



Length 1 — 3 mm. 



A very variable species, not only in size, but in 

 coloration and punctation. The variations may be 

 best described by giving a description of the large and 

 small forms. 



Large Form (2 mm.). — Brownish-red; three broad 

 lines on the mesonotum ; scutellar f ovese, and apex of 

 abdomen above, black ; the legs light brownish-yellow ; 

 the hind femora and tibiae infuscated ; antennae with 

 the basal joints pale brown, the others slightly inf us- 



