122 BRITISH ICHNEUMONS. [ Promethus 

by sweeping low herbage, though occasionally upon the flowers of 
Angelica and at Polygonum ; on 7th September, 1908, I took three or four 
females closely investigating Aphis cra/aegi in my garden at Monks’ 
Soham House, but observed no oviposition. We know nothing of its 
economy ; and little doubt can exist that some error had crept into 
Gravenhorst’s record of Bassus festivus, var. 2 (l.c. 317) “ Neeseo ab Esen- 
beck feminae prodibant e larvis Curculionis polygoni,” though it is strange 
that, in ignorance of this, I should have once or twice observed this 
species on its food-plant. 
8. dorsalis, Holmgr. 
Bassus dorsalis, Holmgr. Sv. Ak. Handl. 1855, p. 367, ?; Brisch. Schr. Nat. 
Ges. Danz. 1878, p.113,¢. B. maculatus, Desv. Trans. Ent. Soc. 1862, p. 216, 
é ¢. Promethus dorsalis, Morl. lib. cit. 1905, p. 429; Thoms. O. E. xiv. 1485, 
(eh Stee 
Black with the legs nearly entirely, and the abdomen except at base 
and apex, red; the latter strongly and falcately compressed in 9? from 
the third segment, with discal black vittae. Length, 43—54 mm. 
This species will be recognised with facility by its triangular face, elon- 
gate cheeks, brunneous and not very slender antennae, nearly hyaline 
wings, the not very short basal segment with its quadrate postpetiole, 
entirely scabrous second segment, the third or even second to sixth of 9 
falcately compressed laterally, and the slender legs. The ¢ has the 
frontal orbits shortly, face and cheeks entirely, stramineous. The hind 
coxae are at least partly black, the basal segment not twice longer than 
broad, the third not stramineous-marked, the mesonotum is smooth and 
strongly nitidulous, and the conformation is much more slender than P. 
festivus, with which the compressed abdomen allies it. 
The 2 sometimes has (1) a subquadrate epistomal mark, small humeral 
lines and the anterior coxae and trochanters, stramineous, with (2) the 
mesosternum rarely pale-lined on either side; and the ¢ segments are 
occasionally apically black. 1 have examined Desvignes’ species in the 
British Museum and find it entirely synonymous. 
Though widely distributed in northern Europe through France, Hol- 
land, Belgium, Germany and Sweden, this species appears somewhat 
uncommon; at all events it is so in Britain, where it is only found in the 
wettest and most boggy situations, always by sweeping reeds. Mousehold, 
Heigham and Brundall, Norfolk (Bridgman); Maker in August, but ap- 
parently rare, in Devon (Bignell); Botusfleming in Cornwall, Nunton in 
Wilts, Lastingham in Yorks and Cheltenham (Marshall); Shere in Surrey 
(Capron); one at St. Kilda (Waterston, Ann. Scot. Nat. Hist. 1906, p. 151). 
I have only found it in June and September at Horsey in the Norfolk 
Broads; Brandon, Henstead marsh, Foxhall pond, and Easton Broad in 
Suffolk. I was surprised to sweep an undoubted 9 of this species from 
oats on the edge of an upland field at Monks’ Soham on zsth July, 1905; 
but there appears no especial reason for the more usual occurrence of the 
species of this genus in damp situations, since they are all doubtless 
Syrphidophagous, unless they be especially attached to hosts preying 
exclusively upon such aphides as Rhopalositphum nyvmphaeae, Linn. or 
Flyalopterus arundinis, Fab. 
