Östen-Sacken: An essay of comparative Chaetotaxy. 125 
oceur among certain Calyptrata (for instance Hydrotaea, Ophyra, Ho- 
malomyia), and just these possess, more than their relatives, the fa- 
eulty of regulating their momentum. Diaphorus (Dolichop.) is also holoptic. 
The further discussion of this subject would draw me beyond 
my present aim, which is a merely practical one, the settlement of 
the terminology of the macrochaetae, and, by that means, the utili- 
zation of a set of characters which, it seems to me, have not yet 
been sufficiently appreciated in descriptive entomology. 
I. Terminology of the parts of the thoraw. 
This terminology refers especially to the Diptera Cyelorhapha; but the same 
sutures and regions of the plearae can be recognized, more or less di- 
stinetly in the Orthorhapha. Some of the sutures sometimes become 
less distinet or obsolete ; for instance in the Tipulidae. 
A. Sutures. 
\ Dorsopleural suture. It runs from the humerus to the 
root of the wing, and separates the mesonotum (or tergum) 
. from the pleura. 
Sternopleural suture. Horizontal suture, below the dorso- 
pleural and parallel to it; it separates the mesopleura from 
the mesosternum. 
Mesopleural suture. Runs from the root of the wing down- 
wards, and separates the mesopleura from the pteropleura. 
B. Portions of the pleura. 
Mesopleura, square piece in front of the root of the wing and 
between the dorsopleural and sternopleural sutures. It answers 
the anterior lateral plate of the mesothorae of Lowne (Anat. 
of the blowfly, Plate 5, f. 5) and to the parapteron of Ham- 
mond (On the thorax of the blow-fly, J. Lin. Soc. XV, Tab. I). 
Pteropleura, situated under the insertion of the wing, and 
behind the mesopleural suture. It is the posterior lateral 
plate of the mesothorax of Lowne and the episternum of the 
mesothorax of Hammond (|. e.). 
Sternopleura; it is that portion of the mesosternum, which, 
from its position, forms a part of the pleura. It is con- 
