336 M. W. R. de V. GRAHAM 



in such cases the characters are obscured. In spite of this I have used the size and 

 shape of the eyes in my key to species, as additional characters for separating the 

 males of microcera (Haliday) from those of graminea Haliday, and the males and 

 females of decipiens sp. n. from those of penetrans (Kirby). The specimens on which 

 these head characters were measured have been left overnight in the vapour of ethyl 

 acetate ; this procedure often ensures that the head retains its normal proportions, 

 and only specimens in which this was the case were utilized. The gaster in many 

 males, and in some females, is more or less strongly compressed after death ; but this 

 feature is not constant, being dependent on the condition of the internal organs in 

 the gaster at the time the specimens are killed. At one stage in my studies on 

 Pirene it occurred to me that perhaps dimorphism might occur in the males of some 

 species, with respect to the relative size of the eyes. This now seems to me unlikely. 



Key to European Species 



(Females) 



i Antenna (Text-fig. 276) with third to fifth flagellar segments large and pro- 



vided with sensilla. Fore wing with speculum, on lower surface, nearly 

 effaced by scattered hairs, on upper surface small and not extending beyond 

 level of middle of marginal vein. Hind tibia without a pecten. Thorax de- 

 pressed, the surfaces of the mesoscutum, scutellum, and propodeum all 

 lying in virtually the same plane ; gaster oval, hardly as long as thorax, 

 ovipositor sheaths not projecting ..... bouceki sp. n. (p. 350) 

 Antennae (Text-figs. 277-278) with at most the fourth and fifth flagellar 

 segments large and provided with sensilla. Fore wing with speculum, on 

 lower surface, at most partly effaced, on upper surface large and extending, 

 as a bare strip below the marginal vein, as far as the stigmal vein. Hind tibia 

 with at least a slightly developed pecten. Thorax often strongly arched 

 dorsally ; if nearly as strongly depressed as in the above, then the ovipositor 

 sheaths project very distinctly, and sometimes the gaster is relatively 

 longer ............ 2 



2 (1) Antenna (cf. Text-fig. 279) with fourth flagellar segment neither anelliform nor 



much shorter than the fifth, with sensilla ...... 3 



Antenna (Text-figs. 277, 278) with fourth flagellar segment anelliform without 



sensilla, often much shorter than the fifth ...... 5 



3 (2) Eyes larger, 1 -3 to 1 -33 times as long as broad. Larger species, 1 -55 to 1 -8 mm. 



Head and thorax with fairly strong greenish to bluish metallic reflections. 

 Fore wing (upper surface) with speculum extending right to the stigmal 

 vein ; beyond the stigma an area which is almost or quite devoid of hairs 

 (see Text-fig. 271) ...... penetrans (Kirby) (p. 341) 



Eyes smaller, 1-4 to 1-45 times as long as broad. Smaller species, 1-2 to 

 1 -4 mm. Head and thorax with weaker metallic reflections, which are 

 usually bluish or bronze ......... 4 



4 (3) Upper surface of fore wing with a bare or almost bare strip which extends from 



the stigma for some distance towards the apex of the wing, but on the under 

 surface of the wing the strip is effaced by scattered hairs Idecipiens sp. n. (p. 342) 

 Upper surface of fore wing without a distinct bare strip in this position (as in 



Text-fig. 272) ....... conjungens sp. n. (p. 344) 



5 (2) Ovipositor sheaths (Text- fig. 273) exserted to a length almost or quite equal 



to that of the hind tibia ; gaster, not counting the ovipositor, nearly 1-5 

 times as long as the thorax, with the tip of the hypopygium very nearly or 



