154 



STRATIOMYIDA^ 



Fill. 133. — Stndiomys potamida 9- x 11. 



pale brownish yellow stripes on the forepart of the thorax which are set well 

 apart and which do not extend half-way to the suture. Scutellum with the 

 long narrow black base as in the male and not with the small middle basal 



spot of S. chamceleon. 



Abdomen duller rustier black than 

 in S. chamceleon, because of the minute 

 rusty black pubescence ; yellow or 

 reddish orange markings more like 

 the male than like S. chamceleon, but 

 the third segment with an entire 

 band on the hindmargin, and this 

 band is narrow all about the middle 

 because the true hindmargin of the 

 segment arches slightly upward,though 

 an imjoressed line runs straight across 

 near the foremargin of the fourth 

 segment in such a way as to give a 

 false impression of Avhat is the real 

 hindmargin ; fourth segment with an 

 entire band on the hindmargin, which 

 is Avidened by an arch upwards at the 

 middle and at the sides ; fifth seg- 

 ment with a semicircular spot on the 

 whole hindmargin, which is some- 

 times a little produced forward at its 

 middle ; pubescence very short and 

 brownish orange on the disc of the 

 third, fourth, and fifth segments. 

 Belly very similar to that of the male, but the basal pair of black spots may 

 extend less towards the sides, and the black bands are sometimes a little 

 narrower, more equal in depth, not pointed at the ends, and not reaching 

 the sides, but in all these points they vary ; pubescence practically none, 

 which is quite different from >S. chamceleon. 



Legs almost as in the male, and as black in the female as in the male 

 instead of being extensively tawny as in S. chamceleon ; pubescence shorter, 

 finer, and all whitish. 



Wings and squamae very much as in the male, but slightly paler. 

 Length about 14-5 mm. 



This species is very distinct from all the other British species except 

 S. chamceleon, with which I have compared it; the narrow second and 

 third pairs of spots or bauds and the short ventral pubescence at once 

 distinguish it. 



>S^ potamida is uncommon in England, but is rather commoner than 

 S. chamceleon. It occurs in extensive marshy or fenny districts, and I 

 have records from Hampshire (New Forest), Sussex (Guestling), Surrey 

 (Guildford), Huntingdonshire (Monk's Wood), Cambridgeshire (Chippen- 

 ham Fen), Suffolk (various localities), Herefordshire (Tarrington, etc.), 

 Hertfordshire (Felden), Gloucestershire (Painswick), Warwickshire (Sutton 

 Park, Eugby). Colonel Yerbury informs me that he has found it common 

 in the New Forest and at Tarrington in Herefordshire, about the end of 

 June and in July. My dates extend from June 13 to August 22. It is 

 recorded from South Sweden and Denmark tluough Central Europe. 



Si/nonymy.—\t is most probable that all references to S. potamida are correct, 

 but it is very probable that many references to S. chamceleon also refer to this 

 species ; Walker's description of >S'. chamceleon undoubtedly refers to this species. 

 Two female specimens in the Hope Museum at Oxford were labelled " splendens," 

 and it is very probable that there is some connection between these and Westwood's 

 fig. 127-1 in his Introduction to the Modern Classification of Insects, vol. ii., 531. 



