A RARE PARASITIC FLY. 33 



Mr. Verrall (the result of some fifty years' collecting). My col- 

 league, who works at Diptera, does not know it, and I have spent 

 some hours .... trying to work it out with books etc., but without 

 success. It is a most surprising thing, especially in view of the 

 locality. I hope that you will be able to secure more specimens, 

 and of both sexes." 



Mr. Austen, at first, was of the opinion that the sex, not only 

 of this particular fly, but also of each of a number of similar 

 specimens that I was subsequently able to send him, was male, 

 but when, later on, at the suggestion of Mr. Collin, who had 

 learnt of my find through Professor Poulton (to whom I had given 

 some specimens for the Hope Collection at Oxford), one of the flies 

 was dissected, leading to the discovery of a perfect egg, it became 

 obvious that the flies that had been captured must be females. 

 And it is a curious and interesting fact that among about fifty 

 specimens of this fly which have been caught (all in the same 

 locality) up to the end of their seasonal prevalence in the early 

 part of June of the present year (1920) not a single individual 

 of the male sex has been secured. I learned, however, from Mr. 

 Collin that he now possesses three specimens of the male in- 

 sect — two taken by the Rev. A. E. Eaton at Seaton (Devon) and 

 the third taken by himself at Long Sutton in Hampshire, all in 

 May 1919, curiously enough the same year and month in which 

 the first specimens (females) were found by myself on Primrose 

 Hill. Mr. Collin further informed me that he possesses female 

 specimens from the following localities : — " Newmarket, Shoebury- 

 ness, and Dunsford (all June captures) ; Cuckmere (Sussex) 

 taken in May ; and a specimen taken by Col. Yerbury at 

 Charlton in April. 



The difficulty as to the sex of my first captures arose from the 

 masculine character of the approximation of the eyes, which is the 

 cause of the very narrow '• irons," which, however, appears to be 

 peculiar to, and distinctive of, the female in this group of An- 

 thomyids — a feature which is well shown in the photograph, and 

 which, so far as I am aware, has not previously been illustrated. 



Nomenclature. — As stated above, Major Austen and his col- 

 league in the Diptera department of the British Museum (Natural 

 History) were unable, at first, to identify this fly, but on calling 

 there on May 28th, 191 9, with some further captures, Major Austen 

 informed me that Dr. P. H. Grimshaw of the Royal Scottish 

 Museum, who had recently paid him a visit, had stated, when the 

 specimens were shown to him, that he recognised the fly, iden- 

 tifying it as Chorto'phila buccatct Fallen, although the species was 

 not (as Major Austen understood him) included in the Scottish 

 collection. 



Shortly afterwards Professor Poulton arranged with Major 

 Austen that Mr. Collin should be afforded opportunity of 

 examining the specimens I had presented to the Museum. 

 for the reason that, as Mr. Collin informed me, his uncle, the 

 late Mr. Yerrall, had suggested that a fly, apparently identical 



Proc. Zool. Soc— 1920, No. III. 3 



