1905.] 175 



if the leg were entirely closed. Whatever the antjle made hy the 

 tibia with the femur, i. e., in whatever position the leg be set, the 

 dorsal surface can always be readily ascertained by turning the fly 

 round until these two portions of the leg appear to be in an exact 

 line with each other, in which ease the outside of the angle will be 

 dorsal. This surface once ascertained, the remainder can be found 

 without further difficulty. 



When there is a row of bristles or hairs extending from the base 

 to the apex, i. e., along the whole length, of any segment (= joint) 

 the term complete may be used. Individual bristles or groups of 

 bristles can be localized according to their distance from the apex or 

 base of the segment in question. Thus we may have a " subapical 

 dorsal " bristle, a " ventral bristle at one-third from base," a " median 

 antero-dorsal " bristle, a " post-median postero-ventral tuft of hairs," 

 and so on. By median is meant half-way between base and apex, 

 pout-median a little nearer the apex than the base, ante-mediaji a little 

 nearer the base than the apex. 



To illustrate the method here advocated for dealing with this 

 branch of descriptive work in Dipfera, I conclude with a description 

 of the cha^totaxy of the legs in the common blue-bottle, Galliphora 

 erythrocephala, Mg. Of course, certain of these bristles are of generic 

 rather than specific value, and therefore in a Monograph should be 

 dealt with in the generic diagnosis and not mentioned in the specific 

 descriptions. The full details are given here so as to employ as many 

 terms as possible in illustration of my scheme. 



Calltphora erytheocephala, Mg. 



Front Legs. — Femora with complete rows of long dorsal, postero-dorsal and 

 postero-ventral bristles, several rows of long and fine posterior hairs, a row of some- 

 what shorter fine ventral hairs in basal half, and anterior surface covered with short 

 fine pubescence. Tibia: with the following subapical bristles : 1 dorsal, 1 postero- 

 dorsal, 1 (rarely 2) posterior and 1 postero-ventral ; a complete row of very short, 

 semi-erect, equidistant dorsal bristles, and a single long and conspicuous postero- 

 ventral bristle at one-third from apex ; posterior and postero-ventral surfaces fringed 

 throughout with short, regular and rather strong pubescence. 



Middle Legs. — Femora with a group of about three subapical postero-dorsal 

 bristles, a single strong anterior median bristle with some shorter and less conspi- 

 cuous ones in basal half, a row of five or six long and stout antero-ventral bristles 

 in basal half, a row of still longer postero-ventral bristles in basal two-thirds, with 

 which are mingled some long fine hairs, ventral surface and apical portions of antero- 

 ventral and postero-ventral surfaces with moderately long, fine hairs. Tibise with a 

 whorl of 6-8 subapical bristles, of which those on the antero-dorsal and ventral 



Q 3 



