NORTH AMERICAN DIPTERA. 249 



but slightly convex, with five visible segments. Legs of moderate 

 size, tibiae without spurs. Wings clear hyaline, veins yellowish, 

 anterior veins crowded, third longitudinal vein branched in the more 

 typical forms, and from the discal cell emits three equal or unequal 

 veins, sometimes the lower veins that arises from the discal cell 

 (fourth longitudinal vein) is faint or rudimentary, and the third and 

 fourth posterior cells are coalescent, but in such cases the discal cell 

 will usually show an angidation indicating its origin. 



Type of the genus 0. ornata Meigen, of Europe. 



In the species placed in this genus there is a greater variation to 

 contend with than in the genus Stratiomyia. In the first or leading 

 character, which distinguishes this from the preceding, viz., "first 

 joint of the antennie less than three times the length of the second ;" 

 there is a gradual lengthening of the first joint from less than twice 

 the length of the second until the full limit is reached, as in 0. jiavl- 

 corniii and O. occipitalis. In the latter the third longitudinal vein 

 is simple, but this character is not confined to those with an unusual 

 long first antennal joint, but is characteristic of a number with nor- 

 mal antennae. Again, in the case of 0. flavicornis and 0. occipi- 

 taiift, which have the same alar and antennal characters ; the eyes 

 of the male of the former are pubescent, while the latter are glab- 

 rous. Rondani founded the genus PseUidoUis on "eyes hairy, type 

 0. elegans vel crnciata Macq." A male specimen of 0. elegaiis 

 before me shows that the first and second joint of the antennae are 

 subequal, and the third longitudinal vein is branched. In 0. viridix 

 Bellardi and 0. ohscum Oliv. the eyes of both the male and female 

 are i)ubescent, third longitudinal vein branched in the former, and 

 in the latter simple. 



Another genus to- which some of the species have been referred is 

 Exchostoma Macq. ; type E. nitida Macq. of southern Europe. I 

 have been unable to make any of our species agree satisfactorily with 

 this genus. Bigot's Exchostoma caliceps I have referred to Loew's 

 0. iiignrodris. Dr. Williston's says " Bigot's species is in any event 

 an Odontomyiay 



A universal study of this and allied genera may prove the necessity 

 of placing some of our species in other genera ; but until this is done, 

 and we have a better knowledge of the American species, such a 

 course would be unadvisable. Some of my determinations may 

 eventually prove to be in error, l)ut I have honestly endeavored to 

 straighten out this neglected group in the hope of furthering an in- 



TRANS. AM. ENT. SOC. XXII. (32) JULY, 1895. 



