DIPTERA. 339 



Here, the third joint of the antennae either borders on an oval or 

 is triangular, or is very long and narrow, and almost lanceolate, 

 as in 



Rai'Hium, Meig. * 

 In the following, or 



PoRPHYROPS, Meig. f, 



It is securiform or triangular, and with a hairy seta ; the first joint 

 is. very short or indistinct. In 



Medeterus, Fisc, Meig., 



This seta is simple, witli the first joint distinct and elongated. The 

 last joint of the antennae, or the palette, is nearly oval. 



M. Macquart has formed a genus — Hydrophorus — with those spe- 

 cies in which the seta is altogether terminal. Those in which the 

 insertion is dorsal, alone compose the genus Medeterus \. 



There, the third joint of the antennae is almost globular. The seta 

 is always hairy. If it be terminal, we have the genus Chrysotus; 

 if it be inserted a little underneath, that of Psilopus ; and, finally, if 

 it arise lower down or near the base, Diaphorus, which genus, by 

 the almost spherical head, nearly entirely occupied by the eyes, in the 

 males, appears to us to lead to the family of the Ptatypezina of 

 Meigen. The wings, ocelli, and some other characters drawn from 

 the parts of the head, contirm those we have described. We cannot, 

 however, enter into similar details here§. 



The Platypezina of M. Meigen, from which Macquart has very 

 properly removed the genus Cyrtoma, and to which we unite that of 

 Scenopina, and his family of the Megacephali ||, consist of Diptera 

 very analogous in their proboscis, antennae and wings, to the Doli- 

 chopi ; but the body is depressed, the head hemispherical and almost 

 entirely occupied by the eyes, at least in the males. The palpi are 

 turned up or withdrawn, cylindrical or clavate, and resembles those 

 of the Notocanthi. The legs are short and spineless, and the pos- 

 terior tarsi frequently broad and flattened. 



These Diptera are very small. M. Macciuart has furnished us with 

 various interesting observations on the habits of several species. 



Some have a seta on the last joint of the antennae. 



Those, in which that seta is terminal, whose eyes are contiguous 

 in the males, and the three first joints of whose jiosterior tarsi, or the 

 first at least, are wide and flattened, form the subgenera 



Callomyia, Aleig., 



Where the first joint alone of the posterior tarsi is di'ated, but is as 

 long as all the others taken together. 



* Meig. and Macquart. 

 •f- Idem. 

 X Idem. 



§ Meig. and Macquart. The genus Lonchoptera, arranged by Meigen with the 

 preceding genera, is greatly removed from them. See the tribe of the Muscides. 

 II We form them into a small tribe, under the denomination of Cephalopsides. 



