„6 URN, ; a Zu Sr 6,5 
2 Li 3 ie , 7 x 
Osten-Sacken: An essay of comparative Chaetotaxy,. 131 
There are often two, sometimes three or more of them, and they are 
inserted between the outer dorso-central row on one side, and the 
humeral callus and the praesutural depression on the other (compare 
below, the notice on the diptera Calyptrata). 
II. Dorso-alar region, between the transverse suture and the 
scutellum on one side, and the root of the wings and the dorso- 
central region on the other. In the Acalyptrata this region only 
contains the group of 
Supra-alar bristles, usually three; one is inserted on the 
post-alar callus (which is often indistinet in the Ortalidae), very near 
the scutellar bridge and almost in a line with the praescutellar 
bristles; the second, is in front of the first, just at the top of a little 
ridge, or ligament /alar frenum), which descends to the root of the 
wing and crosses the supra-alar cavity; the Ziwrd is in front of the 
second, on the edge of the anterior portion of that cavity. These 
bristles are not placed in a straight row; their bases form a triangle. 
A fourth supra-alar bristle sometimes exists in the Örtalidae behind 
the mesothoracie transverse snture and above the posterior post-humeral 
bristle. As far as I can ascertain, this last bristle is distinctive of 
the Section Ortalina, I do not find it in»the other sections of the 
Ortalidae. The diptera Calyptrata often have a series of more than 
three supra-alar bristles along the edge of the anterior supra-alar 
cavity. Even among the Asilidae, the supra-alar bristles form a di- 
stinet group. 
The diptera Calyptrata show other bristles in the same region; 
they often form a longitudinal row of two or three, placed between 
the supra-alar group and the outer dorso-central row. They may be 
called intra-alar bristles. 
III. Dorso-central region,bounded by two imaginary lines, drawn 
from the scutellar bridges forward, and coinciding with a space free 
of bristles, that exists on the outer side of the dorsal rows and that 
is often occupied by a dorsal thoracie stripe. This region contains 
the dorso-eentral bristles, arranged in two or four longitudinal 
rows. They are often wanting in the Ortalidae. In the Dolichopo- 
didae, the intermediate pair of rows is represented by two, sometimes 
only one /LZiancalus) row of peceuliar, minute bristles, which Mr. Mik 
(Dipterol. Unters. Wien 1878 and also Verh. Zool. Bot. Ges. 1880, 
9* 
