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



referred to Trypeta m the wider sense of Meigen and 

 Loew. Ptilona (at least a species from the PhiHppine 

 Islands, which I have before me, and which seems closely 

 allied to P. hrevicornis, v. d, W.) has no ocellar bristles; 

 only one fronto-orbital, inserted very low down, a little 

 above a single fronto-orbital of the lower row. On the 

 thorax: L, no praesutural ; III., only one pair of prae- 

 scutellar bristles. The rest is normal. I hold the 

 absence of the prsesutural bristle (I.) as the more im- 

 portant and decisive character. 



Some African species of Dacus, according to Loew, 

 have no dorso-central bristles at all. (the Asiatic Dacus, 

 which I can compare, have one praescutellar pair). 



Loew {I. c.) describes the lateral bristles of the thoracic 

 dorsum as forming two rows on each side ; I believe that 

 we gain a much clearer view of them when we consider 

 separately those of the dorso-humeral and of the dorso- 

 alar region. As soon as I adopted this mode of grouping 

 I became aware of the importance of the pr?esutural 

 bristle (I.), as characteristic of a true Trypda, and of a 

 bristle behind the suture (II.), which occurs in the 

 section Ortalina, but is wanting in the other sections of 

 thp OrtalidcB. 



In contrast to the complete chgetotaxy of Trypeta, I will 

 give an instance of an incomplete one, in Psila fimetaria. 



Head : Vertical bristles, two pairs of medium size ; 

 ocellar pair very small ; no post-vertical ; no fronto- 

 orbital. 



Thoracic dorsum : I. One praesutural. 11. Only two 

 Bupra-alar, the posterior one is wanting. III. A pra3- 

 scutellar pair. (All the other dorsal bristles are wanting). 



Pleura : No bristles. Scutellum : Two. 



Diptcra Calyptrata. — Cephalic bristles. — The vertical 

 (improperly called soies occipitales by Macquart, Ann. Soc. 

 Ent. Fr., 1845, p. 239), post-vertical, and ocellar {soics 

 stevimatiqucs 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. Among the Taehinidce 

 they afford secondary sexual characters. The facial 

 bristles are also of importance here. 



Pleural bristles. — They are represented b}^ one or 

 several prothoracic bristles above the front coxse ; by a 

 number of mesopleural, and two, three, or four steruo- 



