Östen-Sacken: An essay of comparative Chaetötaxy. 135 
In eontrast to the complete chaetotaxy of Trypeta, I will 
give an instance of an incomplete one, in Psela fimetaria. 
Head. Vertical bristles: two pairs of medium size; ocellar pair 
very small; no postvertical, no fronto-orbital. 
_ Thoracie dorsum. I. One praesutural. II. Only two supra- 
alar, the posterior one is wanting. Ill. A praescutellar pair. 
(All the other dersal bristles are wanting.) 
Pleura. No bristles.  Seutellum. Two. 
Diptera ealyptrata. Cephalie bristles. 'The vertical (impro- 
perly called „soies oceipitales“ by Macquart, Ann. Soc. Ent. 
1845, p. 259), postvertical and ocellar („soies stemmatiques 
of Macquart“), are easy to distinguish among the other hairs 
and bristles; the fronto-orbital bristles (,soies laterales of 
Macquart‘‘) afford important characters in this family and are 
sometimes very numerous, forming one or several rows. The 
facial bristles are also of importance here, 
Pleural bristles. They are represented by one or several 
prothoracic bristles above the fore-coxae; by a number+of 
mesopleural and two, three or four sternopleural, the position 
of which may afford valuable generic characters. Most of the 
Calyptrata , except the Anthomyidae, have a tuft or row of 
bristles on the hypopleura, a region which is destitute of them 
in the other families of diptera. 
The dorso-central region contains the usual four rows of 
bristles, more or less complete; *) the dorso-humeral region one or 
*) The outer row is called by Mr. Kowarz „die inneren Dorsalborsten“ 
(Die Dipterengatt. Lasiops, in den Mitth. d. Münchener Vereins, 1880, 
p- 125, Note), because he applies to the Muscidae the terminology adopted 
by Mr. Mik for the Dolichopodidae. But I believe that, in a terminology 
generally applicable, it will be found much more convenient, even unavoidable, 
to distinguish the inner and outer pairs of rows of dorso-central bristles. 
When the inner rows are very much differentiated,, as is the case in the 
Dolichopodidae, the may be called by the name proposed by Prof. Mik for 
them acrostichal bristles. But it must be borne on mind that these 
bristles represent the inner rows of the dorso-eentral bristles of great many 
diptera; and that it is, for this reason , unbecoming to call „innere dorsal 
