70 STRATIOMYID.^ 



Wings (fig. 94) with a blackish tinge on almost the basal half, reaching up to 

 the end of the two large basal cells and still further into the postical fork 

 cell ; in some lights the blackish part contrasts very strongly with the 

 yellowish or hyaline outer part, the part of the costa immediately after the 

 darkened part being yellowish ; veins strongly marked and blackish on the 

 blackened part, yellowish on the radial and cubital, and faint but distinct 

 on the hyaline part ; cubital vein very distinctiy forked just after the middle 

 of the costal portion of the submarginal cell. S(juamse small, blackish with 

 blacker margins and fairly long blackish fringes. Halteres blackish, rather 

 shining. 



Fig. 94. — Pachygaster atra ? . x 13. 



9 . Frons and face shining black ; eyes separated at the top by about one-third 

 the width of the heacl and gradually approximating until near the antennae, 

 where they are separated by about one-fourth the width of the head, after 

 which they gradually diverge again down to the mouth ; pubescence on the 

 frons light grey and so minute as to be hardly visilde, but obvious fairly 

 dense and greyish black on the flat face ; back of the head shining black, 

 puffed out on the lower part to almost half the width of the eyes, and even 

 on the upper part widely and conspicuously inflated, and all bearing a slight 

 greyish pubescence. Antennas all dull orange ; arista long, pale yellowish. 



Thorax and scutellum almost as in the male, but bearing only short 

 decumbent grey pubescence, which is however longer and greyer than in 

 P. Leachii. 



Abdomen as in the male, but with short universal decumbent grey 

 pubescence ; ovipositor (when exserted) long and narrow, orange. 



Legs as in the male. 



Wings with the blackish basal half more contrasted against the subsequent 

 pale part with its yellow anterior veins. 



Length about 3-5 mm. 



This species is easily distinguished from all the others, except P. 

 tarsalis, by the blackish tinge on the basal half of the wing, while from 

 P. tarsalis it may be known by its differently colored antenna^ and its 

 much more inflated back of the head. P. tarsalis is also a larger stouter 

 insect, and has the blackened basal part of the wing usually less pro- 

 nounced, and has a pair of slightly silvery shimmering spots on the frons 

 in both sexes, though most distinct in the female; those female speci- 

 mens of P. tarsalis which have orange antennse may be distinguished by 

 the larger size of the antennse, besides other characters. 



P. atra is the commonest species of the genus, but yet is by no means 

 common. I once found the female occurring in numbers on the windows 

 of the hotel noar Weybridge Station, and on July 8, 1904, the males 

 were swarming by hundreds about two bushes out on the open part of 

 Chippenham Fen, when four females were also obtained but probably 

 through sweeping the bushes; Mr C. Morley once found it abundant on 

 bracken (Pferis aquilina) at Foxhall in Suffolk. I am inclined to think 

 that the life of the male is a very short one. My records are not so 

 numerous as I expect they ought to be, as 1 have notes from only Pevon- 

 sbire,Dorset, Kent, Middlesex, Suffolk, Cambridgeshire, Hereford, Glamorgan, 

 and Haddington, from May 19 to July 27. Tt is recorded from extreme 



