152 STRAT10MYID.E 



practically united at the middle; fifth segment with a narrow black line, 

 which is still more narrowed at the sides and at the middle, and which does 

 not quite reach the sides ; pubescence similar to that of the male but a little 

 shorter and rather more sloping. Ovipositor composed of a small transverse 

 brown plate which is hidden under the hindmarginof the fifth dorsal segment, 

 and with a middle pair of small brown lamellae which project just beyond the 

 hindmargin of that segment. 



Legs rather similar to those of the male, but the base of the front femora 

 and nearly all the posterior femora tawny ; the middle femora have a rather 

 long and broad irregular dull black ring just after the middle, which is 

 considerably extended beneath and towards the front, even sometimes to nearly 

 the whole length, leaving at the same time a comparatively narrow dorsal 

 band between the middle and the tip, but even that may be rather obscurely 

 extended to the middle ; on the hind femora the shining black band is better 

 defined but still is considerably extended beneath. 



Wings as in the male. Squamae with rather shorter pubescence. 



Length about 14-5 mm. 



This species has only one close ally in England, S. potamida, and I have 

 specially contrasted that with it. 



S. chamceleon is rather rare in Britain, as the records of so large and 

 conspicuous a fly are sure to be noted in most cases. I know it has 

 occurred in Devonshire (Bovey Tracey), Dorset (Blox worth Heath), 

 Hampshire (Lyndhurst), Cambridgeshire (Chippenham Yen), Norfolk 

 (West Runton), Oxfordshire (Ogley Bog near Shotover), and Leicestershire 

 (Owston Wood) from the end of June to September 9 ; most of the old 

 records may refer to S. potamida, except those of Duncan in 1837, as he 

 fully recognised the distinctions between the two species, and he wrote of 

 it as occurring in most parts of England and Scotland, giving specially some 

 localities near Edinburgh. My own experience of it is mainly limited to 

 Chippenham Fen, where I have taken it as early as July 6 and as late as 

 August 23 ; it occurred on large Umhelliferm, upon which it could be seen 

 a long way off, and though sluggish and easy to catch from the flowers it 

 created a great disturbance when in the net. The metamorphoses are well 

 known, and the larva, which is one of the " rat-tailed maggots," lives in 

 muddy water, in which it can float or sink at will ; it is believed to feed on 

 minute Infusoria ; the eggs are said to be laid on the under side of the 

 leaves of Alisma plantago, and to be arranged like tiles on a roof, one being 

 laid partly over another. It is recorded from Sweden to the Alps. 



Synonymy. — Linne's and De Geer's descriptions seem to point more to S. j)otamida 

 than to this species, but as it is impossible to be certain upon this point it is 

 sufficient to accept Meigen's apportionment of the names. Walker clearly described 

 »S'. potamida under the name of S. chamcdeon and openly gave *S'. potamida Meigen 

 as a synonym, but he did not seem to have recognised the true S. chamceleon at all. 



2. S. potamida Meigen. Very much hke S. chamceleon; but the 

 yellow markings on the third abdominal segment are linear and pointed 

 at their inner ends ( c? ) or form an entire band ( ? ), and on the fourth 

 segment form an entire band in both sexes. 



A large conspicuous fly (fig. 125), which is almost as hand- 

 some as S. chamceleon. 



S. Compared with *S' chamceleon the head is large (being comparatively the 

 largest of our four species), the sides of the face and frons are more rounded 



