1881. 103 



They may be distinguished by the following characteristics : the face is more 

 prominent in R. ambigua than in R. divisa, and of a more brilliant silvery-white 

 colour ; the three longitudinal broad black stripes present on the thorax of both 

 species, are separated by much more distinct white interspaces in R. ambigua than in 

 R. divisa ; and the sides of the thorax are of a more brilliant shining white colour 

 in the former than in the latter. The scutellum is grey, with the apex shining 

 black, in R. ambigua while it is of an uniform grey colour in R. divisa. The abdo- 

 men has a longitudinal black dorsal stripe in both species, but it is much wider in 

 R. ambigua than in R. divisa, and of nearly equal width in its whole length, ex- 

 tending over each segment to the apex. In R. divisa it is moderately wide over the 

 first segment, but gradually becomes narrower, and terminates in a fine line, or 

 becomes indistinct, at the hinder margin of the third segment. The apex of the 

 abdomen is shining black in R. ambigua, but grey in R. divisa. The sub-anal 

 appendages are very different in the males of the two species, affording very charac- 

 teristic points of distinction ; in R. ambigua they form a large projecting complicated 

 hairy mass, under the third and fourth abdominal segments ; while in R. divisa 

 there are two long brown horny lamellae, extending forward from the under-surface 

 of the apex, arid covering the rest of the male organs, which are much smaller and 

 less hairy than in the former species. The third and fourth longitudinal veins of 

 the wings slightly diverge from each other in R. ambigua, while they run quite 

 parallel to each other in R. divisa as they approach the margin. The posterior tibiae 

 are ciliated on their outer and posterior surfaces with a number of long and short 

 bristles of uneven lengths in R. ambigua, while in R. divisa there is a row of very 

 short stiff hairs of equal lengths, extending along the whole outer surfaces of the 

 tibiae, and three long bristles in addition, one placed in the centre and one at each 

 extremity of the tibia. 



H. CAUDATA, Zett. 



This species may be known from either of the preceding by its having two lateral 

 tufts of hair, one on each side of the anus, on the under-surface, and another central 

 tuft at the end of a projecting process, placed in front of the large hairy genital 

 protuberance, beneath the penultimate abdominal segment. The abdomen is marked 

 in the same way on the dorsum as in R. ambigua, but is more hirsute. The posterior 

 tibia? are armed as in R. divisa. 



I captured several males of this species in 1874 on the margin of Lake Winder- 

 mere ; I have not met with it in any other locality. 



H. BRTTNKEIFRONS, Zett. 



The female only of this species has been described ; neither Zetterstedt nor 

 Eondani knew the male. I found one female at Silverdale, Lancashh*e, in May, 

 1881, and have another which I found in a collection of Diptera made by the late 

 E. Walker. 



H. ASTHOMYIEA, Eoild. 



This well-marked and pretty species has not been noticed by any author except 

 Eondani, who found it rarely in Italy. Herr Kowarz has met with it in Austria, 

 and it is generally diffused and by no means rare in England ; so it probably occurs 

 in other parts of Europe, but has been overlooked. 



