4 DIPTERA OF NORTH AMERICA. 



the sections of Nemocera and Brachycera. The fact known long 

 ago, that in some genera of Stratiomydcc and Tabanidce the joints 

 of the flagellum not being closely compressed, do not form a com- 

 pact joint, has been rather neglected in this respect, perhaps be- 

 cause the Stratiomydee and Tabanidce, by their whole organization, 

 are rather remote from the Nemocera, and have so strikingly pecu- 

 liar characters as individual families, that their comparison with 

 the Nemocera has scarcely been thought of. The case was dif- 

 ferent when* a similar structure was observed in the family of Xylo- 

 phagidce. After I had myself first pointed out the genera Electro, 

 and Chrysothemis, discovered by me in Prussian amber, Mr. Hali- 

 day found the still more surprising North American genus Rachi- 

 cerus. I shall have hereafter to mention a second North American 

 genus of Xylophagidce, which has the flagellnm of the antennae not 

 annulated, but really many-jointed. All these facts, however, are 

 not sufficient to compel us at present to give up the separation of 

 the Nemocera and Brachycera. 



Many authorities have likewise objected to uniting under the 

 head of Brachycera all those families which cannot be referred 

 to the Nemocera, especially and with the fullest reason, to the 

 union of the Hippoloscidce with, the other Brachycera, since 

 both the history of their development arid their internal and ex- 

 ternal anatomy essentially differ from them. They can only be 

 considered as a third section, co-ordinate to the Nemocera and 

 Bracliycera, and having the same systematic value, and may be 

 named Coriacea, or they may be opposed to the other two together 

 as equivalent, and consequently be comprised under the name of 

 Eproloscidea, that of Proboscidea being left to the two other sec- 

 tions. I intend to follow the first of these two arrangements. 



Of the families which I shall hereafter enumerate as belonging 

 to the Bracliycera, the Plioridce alone have occasioned some doubts 

 about their title to this place, founded, if I judge correctly, on 

 the abnormal structure of their antenna? ; these are considered as 

 one-jointed, with the terminal bristle consisting of several joints. 

 .Judging by the anatomical structure, I for my part am unable to 

 see in the joint, which is pre-eminently developed and forms the 

 main body of the antennae, more than the first joint of the flagel- 

 lum, its peculiarity arising from the soldering together and stunting 

 of the*two joints of the scapus, the covering of which is moreover 

 less horny than in the other families of Brachycera. This differ- 



