504 C. E. Osten-Sacken's essay on 



separated by a suture. It answers to the side of the 

 metasternum of Lowne, and the epimeron of the meso- 

 thorax of Hammond, {d of the figure). 



Metajjleura, immediately above the hypopleura, and 

 behind the pteropleura ; a more or less convex, tubercu- 

 lar piece between the root of the wing and the haltere : 

 in the Asilidce it bears a characteristic fan-like row of 

 bristles ; between it and the metanotum the callus 

 metanoti lateralis of Loew (Mon. N. A. Dipt., i., p. xiv.) 

 is placed, {e of the figure). 



C. Other Terms for Parts of the Thorax. 



Scutellar bridges, the small ligaments which on each 

 side of the scutellum connect it with the mesonotum, 

 crossing the intervening suture. (Prof. Mik proposes to 

 call them in Jjntin, jiifinm scutellare). 



Prcesutiiral dejn'cssion,' a triangular depression usually 

 existing in the angle formed by the transverse meso- 

 thoracic suture and the dorso-pleural suture ; a slight 

 swelling at its bottom is the pr(ealar callus. 



Prcealar and j^ostalar callus ; more or less distinct tu- 

 bercles which often exist, the former in front of the 

 wing, the latter between its root and the scutellum ; 

 they often bear characteristic bristles. (In my former 

 writings I have occasionally used the term prceseutellar 

 callus for post-alar, but the latter is preferable). The 

 word callus, here as elsewhere, is taken for the German 

 Seliwiele, in the sense of tubercle, swelling, and not 

 merely of a hardness of the skin (which is the sense of 

 callus in Webster's Dictionary). In this, as in other 

 cases, I have preserved the terminology adopted by Loew 

 in the Monogr. N. A. Dipt., vol. i. (1862). 



Supra-alar cavity, an excavation of the mesothorax 

 above the root of the wing, along the edge of which the 

 supra-alar bristles are inserted. It is divided into an 

 anterior and a posterior portion by a small ligament, 

 which runs towards the root of the wing {alar frenum). 



11. — The Terminology of the Bristles. 



1. — In studying the chfetotaxy of the Diptera it was 

 natural for me to begin with those families in which the 

 arrangement of the bristles is the most simple, that is, 

 with the Diptera Acalyptrata. After having adopted a 

 terminology for these, the next step was to ascertain 



