1900.] 199 



SOME NOTES ON THE BEITISH SPECIES OF THE 

 GENUS NORELLIA. 



BY COL. J. W. YERBUBY, late R.E., F.Z.S. 



Having during the past three years devoted some time to the 

 British species of the genus NorelUa, it may be useful to draw atten- 

 tion to some of the conclusions [ have arrived at, particularly as these 

 conclusions ai-e opposed to some generally accepted ideas on the 

 subject. 



While in Scotland during the year 1898 I took several female 

 specimens of a Norellia which agreed so perfectly with Becker's and 

 Meigen's description of N. striolata that I had no hesitation in refer- 

 ring them to that species ; this identification was confirmed later on 

 by Mr. Austen (one of my female captures stands at the present time 

 under the head of N. striolata in the B. M. Collection), and has 

 apparently since been followed by Mr. Grimshaw, who records (Ann. 

 Scott. Nat. Hist., Jan., 1900, p. 28) a specimen taken by me at Avie- 

 more as belonging to this species. To my surprise, however, I found 

 that all^'the male specimens taken on the same dates and in the same 

 places with the above females belonged to N. Jlavicauda, and that no 

 males at all agreeing with the description of N. striolata ^ had been 

 captured. This result struck me as being so strange that 1 deter- 

 mined to get together a long series of the genus from various localities 

 for further examination. AVith this object I amassed during 1899 

 some eighty specimens representing the so-called species, spinimana, 

 Jiavicauda, nervosa, and striolata. This long series showed a complete 

 gradation from the form (^spinimana) with a bright reddish-yellow 

 thorax bearing two fine black lines, through the form (Jiavicauda) in 

 which the lines have become broader and lighter coloured (brownish- 

 drab), eventually coalescing and leaving only the points of the 

 shoulders and the scutellum of the original red, on to the form 

 {nervosa, Meade, nee Meigen) in which the brownish-drab colour 

 covers the whole disc of the thorax and swallows up even the shoulder 

 points and the scutellum. As the distinctions given in Becker's table 

 (Berl. Ent. Zeit., xxxix, 189i, p. 124) for the separation of these four 

 species depend mainly on the colour and striping of the thorax, and as 

 m-^ specimens showed no definite points for division in that respect, 

 but appeared to merge the one into the other, I was forced into the 

 conclusion that our English specimens were all forms of one species. 

 I was so impressed with this idea that when at Newmarket last 

 September I asked Mr. Verrall to examine all my specimens to see 



