NATURAL CHARACTEE. 53 



of the orbit, two or three stouter bristles, but generally less stout 

 in the Dacina than in the Trypetina, whereas in the males of some 

 Trypetina they are thickened into spines, or even inserted upon 

 lateral processes. The little crescent cut off by the frontal fissure 

 is often very distinct, though never very large. The antenna? are 

 directed downwards, the third joint elongated or long ; the bristle 

 nearly bare, or with a very short pubescence ; only in a few spe- 

 cies it has longer hairs, but is never pectinated. The face shows 

 below each antenna a flat excavation, more deepened in those few 

 species which have a keel in the middle of the face ; the anterior 

 border of these excavations forms a more or less distinct eleva- 

 tion, and sometimes almost a keel. The cheeks are more or less 

 hairy; in a few Trypetina the furthermost hairs almost have the 

 appearance of vibrissas, which, however, are never present. All 

 more naked species have also less hairy cheeks. The proboscis 

 is never much thickened ; the suctorial flaps are sometimes very 

 short and rather broad, sometimes rather long, sometimes of an 

 extraordinary length, as for instance in the species of Myopites 

 Breb., where they seem to become much stouter, which was the 

 reason why a species of Myopites was placed by Fabricius in Sto- 

 moxys. The prolongation of the suctorial flaps is proportionate 

 to that of the stem ; not unfrequently in most nearly related species 

 the structure of the proboscis seems to be very different ; but on a 

 closer examination this difference appears not to be essential, and 

 cannot even always be used in characterizing the small genera into 

 which the genus Trypeta Meig. has been divided. Among the 

 Dacina I have never seen a species with a very prolonged pro- 

 boscis. The oral cavity is large, sometimes very large and widened, 

 and not seldom a little prolonged at its anterior border ; its form 

 depends very much on that of the proboscis ; for in those species 

 which have a very long proboscis, the anterior border of the 

 mouth is usually also much more projecting. The palpi are either 

 more applied to or more laid upon the labium, when it is retracted 

 into the mouth-hole ; their form is more or less spatulate, and 

 generally more elongated in those species which have a long pro- 

 boscis than in those with a short one. The clypeus owing its 

 origin to a duplication of the skin which connects the stem of the 

 labium with the border of the mouth is narrow, and being con- 

 cealed within the mouth-hole can only be seen anteriorly in those 



