506 G. R. Osten-Sacken's essay on 



A. Cephalic Bristles.* 



Vertical bristles, so called from their position on the 

 vertex ; there are two pairs of them, the inner and the 

 outer one ; both are inserted more or less behind the 

 upper and inner corner of the eye. They are either 

 erect or the bristles of the inner pair are converging, 

 those of the outer diverging. These two pairs of bristles 

 are the most persistent of all, among the Acahjptrata, 

 although even they disappear in some genera. (For the 

 identification of these bristles I recommend the head of 

 Tetanocera). 



Post-vertical pair of bristles, in the middle of the upper 

 part of the occiput, behind an ideal straight line, con- 

 necting the vertical bristles of the inner pair. They are 

 generally small or absent ; large and conspicuous in 

 Tetanocera. 



Ocellar imir of bristles, on the ocellar triangle ; they are 

 always diverging and pointing forward ; often wanting. 



Fronto-orbital bristles, placed on each side of the front, 

 near the orbit, immediately below the vertical bristles, 

 on the little stripes which generally run down from the 

 vertex on each side of the front of the Ortalidce. There 

 is only one pair of them (on each side), or two, one below 

 the other ; often none. In the Ortalidce they are gene- 

 rally placed high on the front; in other families {Teta- 

 nocera, Sapromyza, &c.) they reach lower. 



'■•' The terminology of the parts of the head is confused and con- 

 tradictory in different writers, and for this reason an exi)lanation is 

 necessary. Frontal orbit I call the whole interval between the 

 frontal stripe and the eye. The term is not always appropriate, 

 esj^ecially for the Tacliinidce, where that interval occupies the 

 greater part of the front ; but I prefer to retain it rather than to 

 change the terminology adopted by Loew in the Monogr. N. Am. 

 Dipt., vol. i. These parts are the Wangenschcitelplatten of Prof. 

 Brauer (Die ZweiHiigler des Kais. Mus. in Wien), and the optica 

 frontis of Eob. Desvoidy. When there is no distinct frontal stripe, 

 as in some Acalyptrata (for instance, the Ej^hydridcc), the dividing 

 line of the orbits is merely an ideal one. There is no sei)arate term 

 in Loew for the portion of the face, very distinct in many Cy- 

 clorhajjha, between the lower part of the fi-ontal fissure and the 

 antennal foveae ; a stripe which generally contains, in the Calyp- 

 trata, a vertical ridge bearing a row of bristles. We have no other 

 choice but to use llobineau Desvoidy's term faclalium (plural, 

 facialia), also adopted by Wallier. This piece is very distinct in 

 the Ephydridcr, and, althougli level here, it is bounded by sutures 

 and often bears a row of hairs. Stenhammar calls it cpistomatis 

 partes laterales, which is too ci;mbroixs for use. 



