Ss Zar ne A 
Osten-Sacken: An essay of comparative Chaetotaxy. 129 
each side of the front of the Ortalidae. There is only one of 
them (on each side), or two, one below the other; often none, 
In the Ortalidae, they are generaliy placed high on the front; 
in other families (Tetanocera, Sapromyza ete.) they reach lower. 
Lower fronto-orbital bristles, occupy the lower part of 
the front, above the antenna, along the orbit. They are diffe- 
rentiated from the ordinary fronto-orbital bristles in not being 
quite in a line with them, that is, in being inserted either a 
little nearer to the orbit (Trypetidae), or a little farther 
(Scatophagidae); they also differ from the upper fronto-orbital 
bristles in being smaller, or inserted closer together, They 
are not of frequent occurrence, 
Vibrissa (Meigen, Vol. I, XXIX) a stout bristle on the lower 
end of the facialia, immediately above the peristomium and 
below the antennal foveae, on each side, often accompanied 
by some smaller bristles. Vibrissae are characteristic of some 
families; they are wanting in the Trypetidae and Ortalidae. 
Faecial bristles, *) imserted in a series, on each side of the 
middle portion of the face, above the vibrissae, along the fa- 
cialia; they are especially conspicuous in the Tachinidae. They 
are rare among the Acalyptrata; the Ephydridae, for instance, 
have some weak ones on each side of the face, 
In some genera other characteristic bristles occur, less 
persistent than those enumerated above, that is, appearing 
' sometimes in one species and disappearing in another, in the 
same genus. Such is an oceipito-orbital bristle, in some 
Ortalidae, inserted on the posterior orbit of the eye; one or 
several genal bristles, on the cheek, near the lower corner 
of the eye etc. A row of bristles along the posterior orbit 
of the eye in the Dolichopodidae, have been aptly called by 
Mr. Loew eilia of the posterior orbit, similar bristles 
*) Rondani (Prodr. III, p. 244) calls the facial bristles selae orales, 
a term which is misleading, because oralis means belonging to the mouth, 
as well as belonging to the face. (We have the oral organs, oral margin, 
both referring to the mouth). Rondani’s other terms setfae verticales, ocel- 
_ lares, frontales, are the same as mine, 
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