40 COSTA RICAN DIPTERA 



there has been practically no work clone on the Central American 

 species, instead only isolated descriptions of new forms. Conse- 

 quently the literature gives very little trouble. Furthermore, 

 the writer has examined the types of most of the known species 

 occuri'ing, or likely to occur, in Costa Rica. In view of the 

 forthcoming revision of the American Ephydridae, of which two 

 papers have already appeared,^ the species in the present paper 

 are not as fully treated as they otherwise would have been. How- 

 ever, the descriptions of the new forms are full enough to enable 

 the student to recognize them, and pertinent notes are given on 

 most of the others, while analytical tables, where possible, are 

 given of all the forms treated. 



This family, as with the majority of the Acalyptratae, includes 

 species most of which are so small, that a microscope is neces- 

 sary for their thorough study. In consequence it will not be 

 a very inviting study to many; although the field offers more 

 opportunities for real constructive work than many other groups 

 possessing larger individuals. The writer makes constant use of 

 a Zeiss binocular microscope, with a combination giving a mag- 

 nification of about forty-five diameters, Avith an occasional use 

 of a higher power. 



As to the systematic limits of the family, little can be said, for 

 much exhaustive study will be necessary'' before the families of 

 the Acalyptratae can be thoroughly understood. However, the 

 species of this family, as here understood, may be recognized by 

 the structure of the head, especially of the face. There are no 

 vibrissae or vibrissal angle or ridge; the parafacials (the areas 

 next to the eyes), parafacial ridges and groves are never converg- 

 ing below, but always extending posteriorly and ending at the 

 lateral oral margin; the mesofacial area is always convex, some- 

 times greatly swollen, at most with only a weak carina, except 

 between the antennal foveae in some species. There is usually 

 a series of bristles on each side of the face, which below are con- 

 centric with the orbits, while above they maj^ continue so, or, 

 may converge, crossing the face and become contiguous. In the 

 latter case the mesofacial area is prominent and setulose (char- 

 acteristic of the subfamily Ephydrinae). The auxiliary vein 



3 Trans. Amer. Ent. Soc, xlii, 101-124, 1916 (Paralimna). Trans. Amer. Ent. 

 Soc, xliii, 27-66, 1917 {Notiphila and Dichaeld). 



