SPIDER FLY ; GROUSE FLY. 67 



killed birds when driving early in the season. There appeared to be 

 generally two or three on each bird." 



Ornithomyia avicularia is of the family of Hippohoscida, but is dis- 

 tinguishable by several easily observed points from Hippohosca equina, 

 noticed in the preceding paper. For one thing, it is about one-quarter 

 less in size than H. equina (Horse Forest Fly), which is from three 

 and a half to four lines long, whereas 0. avicularia (Grouse Fly) is 

 from two and a half to three lines in length. Also, in addition to the 

 compound eyes possessed by both species, 0. aviculari't has three 

 oceiU, simple eyes (specks on the top of the head), whereas H. equina 

 has none. 



There is also a very characteristic difference in the structure of the 

 claws of the two species. In both species each foot is furnished with 

 two claws, but in equina each claw is divided into two portions, in 

 avicularia into three. 



A reference to the figure of the claw of H. equina at p. 53 in the 

 preceding paper, and in the frontispiece, will help to make the above 

 differences clear. It will be seen there that the claw of equina is 

 divided into one long curved portion, with another, a lumpy obtuse 

 portion, attached, which is about half the length of the curved and 

 pointed part. In regard to Ornithomyia, it is mentioned by Dr. J. E. 

 Schiner in his account of the characteristics of this genus,* that " the 

 claws have two side claws, and thus are three-toothed.^^ 



On examining Mr. Wheler's specimen with a quarter-inch object- 

 glass, I found the uppermost longest division of the claw rather more 

 slender and flatter than in equina, and very sharply pointed ; the next 

 division (corresponding with the thumb-like or lumpy division in 

 equina) much longer and somewhat narrower in proportion than that 

 of equina (about two-thirds of the length of the pointed portion), and 

 very obtusely ended. The third division was not so well defined, 

 apparently from the balsam or preservative medium having soaked 

 into it and made it partly transparent. But this was dark at the 

 base, and where I was able to get what seemed a correct view, it was 

 merely a small body about the width of the other blunt claw, but only 

 about half its length, and ending in a very blunt point, so as to give 

 it almost an oval shape, also there was a raised vein, or ridge, and 

 one or two lesser elevations running along it longitudinally. From 

 want of sufficient specimens to examine, I was not able to make out 

 the nature of this division or lobe of the claw quite clearly, but it 

 appeared as if, although horny, it was not of such exceedingly hard 

 substance as the other divisions of the claw, and I only submit an 

 imperfect description. 



* 'Fauna Austriaca (Diptera),' von J. R. Schiner, ii. Theil, p. 646. 



