92 PROCEEDINGS OF THE NATIONAL MUSEUM. 



arranged in patches as in the Oestridae. In some specimens, owing to 

 the two surfaces being preserved on a single plane, the surface appears 

 to be more completely covered than it actually was in life. The 

 structures are not more delicate than in some Oestridae. Scudder also 

 remarks that it is difficult to understand how such masses of Oestrid 

 larvae could accumulate at one place. This, however, is quite possible 

 if they infested gregarious animals, though we must agi'ee that the 

 infestation seems to have been remarkably heavy. 



Scudder's species came from the Chagrin Valley, White Eiver, 

 Colorado. This locality is certainly Eocene, but perhaps not con- 

 temporaneous with the Green River beds of Wyoming. The present 

 material is assigned to the Green River, following the indication of 

 the label. Since the above was written a large quantity of material 

 containing H. ascarides has come to hand, collected at Hay Gulch, 

 Colorado (D. E. Winchester and others, U. S. Geological Survey). 

 The precise locality is southeast quarter of section 36, township 1 n., 

 range 96 w. 



EMPIS PERDITA, new species (Empididfc). 



Length 7.5 mm.; wing almost 7 mm. long, the apical and costo- 

 apical region faintly dusky; structure quite normal for the genus. 



Hind femora 3 mm. 

 long, not incressate, 

 thinly clothed with 

 black bristles, but 

 ^ • with a longitudinal 



Fig. 2.— EMPIS perdita. a. End of tuikd vein, h. End of bare band ; anterior 

 FIRST BASAL CELL. fcmora 2 mui. long. 



The following measurements are in microns: Height of head, 

 about 990 ; length of proboscis, about 1680 ; length of antennae (ex- 

 cluding style), about 640. Venation essentially as in Empis tri- 

 gramma, the nervure separating the first basal cell from discal 

 strongly arched, longer than the anterior cross-vein. Measurements 

 in microns : End of second vein from end of upper branch of third, 

 225 ; first basal cell on first submarginal, 320 ; discal on second poste- 

 rior, 176; discal on third posterior, 512; discal on second basal, 288; 

 lower side of second basal beyond tip of anal, 384. 



Miocene shales of Florissant, Colorado; received from Mr. L. E. 

 Daniels, who obtained it from Mr. J. C. Carr. Easily known from 

 the previously described species of Empis from Florissant by its 

 much larger size. 



In the original account of Empis -forksantana Cocke relP the 

 figure of the discal cell is upside down. 



iProc. Acad. Nat. Sci. Phila., 1914, p. G40. 



