48 DIPTERA OF NORTH AMERICA. [PART III. 



distinguished by the first abdominal segment being beset with 

 bristles. This character, as well as the somewhat advanced posi- 

 tion of the anterior ocellus, remind of the Richardina. The 

 face is rather short and somewhat excavated. 



The last genus which I place among the Platydomina forms the 

 transition from this group to the Cephalina, and shows a good 

 deal of approximation to the genus Cephalia As the typical spe- 

 cies of this genus I consider Cephalia myrmecoides Loew. Be- 

 sides the want of a mesothoracic bristle, this genus differs from 

 the true Cephalise in the fact that the first abdominal segment is 

 so coarctate in its middle that its anterior part forms a knot- 

 shaped swelling ; moreover, the shape of the body is still more 

 slender ; the wings still narrower and still more cuneiform 

 towards the basis, so that the anal angle and the alula disappear 

 entirely, whereas in Cephalia, there is at least a rudiment of 

 them. The statements which Rob Desvoicly makes about his 

 genus Myrmecomyia render it probable that the above-mentioned 

 species belongs to this genus. Certainty in this case is not pos- 

 sible, without the comparison of the species upon which Rob. 

 Desvoidy established the genus. Not wishing to run the risk of 

 introducing a useless generic name, I prefer to use the name of 

 Myrmecomyia for my species. The pleonastic name which the 

 species thus obtains, Myrmecomyia myrmecoides, is not good, 

 but may be tolerated in view of the fact that nothing is more 

 like an ant than this dipteron. 



A review of the genera which I placed among the Platysto- 

 mina shows that, besides the bristles upon the first longitudinal 

 vein, and the absence of prothoracic and mesothoracic bristles, 

 which define this group, these genera have the following charac- 

 ters in common : The oral opening is very large ; the clypeus 

 generally very much developed, and the proboscis proportionally 

 stout ; the third antennal joint is elongate ; the thoracic dorsum 

 bristly upon its hind part only; the female abdomen has four 

 segments, as the fifth is either altogether wanting, or only rudi- 

 mentary and then completely hidden under the fourth segment. 



Third Section: Cephalina. 



I call this group after the genus which was first made known 

 in it. It differs from the Platystomina in the presence of a 



