28 D1PTERA OF NORTH AMERICA. [PART JJI. 



neighborhood of Pyrgota, with which it also agrees in the small 

 development of the clypeus. However, the ocelli are fully 

 developed, and the structure of the head is rather like that of the 

 true species of Dacus, as Dacus oleee, etc., so that it might per- 

 haps be considered as a genus of this group, in which, in con- 

 formity to the striking shortness of all the hairs of the body, the 

 lateral bristles of the front have disappeared. This supposition 

 seems confirmed by the scutellum which has only two bristles at 

 the tip ; and the uncovered last abdominal segment of the female, 

 which is generally wanting in the Dacina, or is altogether con- 

 cealed under the preceding segment, is not a positive objection, 

 as this segment is very much abbreviated and much less horny 

 than the preceding ones, and thus can very easily be concealed 

 In the living insect. 



Among the scattered publications of various authors many 

 forms may be found which belong to the Ortalidse. I purposely 

 omit what I know of them, especially the gradually published 

 species of the genera already discussed by me. It is not in my 

 power to collect the residue, and I doubt whether such a work 

 would materially alter the limits of the family Ortalidse as they 

 have resulted from the preceding discussion. 



NATURAL CHARACTERS OP THE FAMILY ORTALID^B. 



If we ask now what we have to erase or to modify in the cha- 

 racters of the original genus Ortalis, in Meigen's and Wiede- 

 mann's sense, in order to obtain the characters defining the whole 

 family, the answer will be that it is very little indeed. In the 

 first place, the mention of the pilosity of the front must be modi- 

 fied a little, as there are genera among the Ortalidse which have 

 no other bristle before the bristles of the vertex. Next to that, 

 the description of the structure of the feet has to be changed 

 thus, that in most genera they are short and strong, but in some 

 rather elongate. In the third place, the statement about the 

 female abdomen must be modified by saying that it has generally 

 five segments, but that the fifth is very often shortened and con- 

 cealed under the fourth, and that, in some cases, it entirely dis- 

 appears, and then the abdomen has only four segments. In the 

 fourth place, the introduction of Pyrgota and of the related genera 

 in the family, requires a modification in the statement about the 

 structure of the ovipositor, which is not flattened here ; the chief 



