ART. 13. DESCRIPTIONS OF FOSSIL INSECTS — COCKERELL. 5 



The following measurements are in microns : Length of hind tibiae 

 1,230, of hind basitarsus 720; end of auxiliary to end of first vein, 

 800; anterior cross- vein to base of discal cell, 1,120, to end of discal, 

 830 ; length of anterior cross- vein, 80 ; apical side of discal cell, 608. 

 The discal cell is shaped like the butt of a gun. 



Horizon and locality. — Green River Eocene; head of East Alkali 

 Gulch, about 8 miles south of De Beque, Colorado (John P. By ram,. 

 1922). 



H olotype.— C^t. No. 69175, U.S.N.M. 



A remarkable little fly, which I at first thought to refer to the 

 Anthomyiidse, but it appears to be acalyptrate, and the venation 

 agrees better wnth Trypetidae. In certain respects, it agrees with 

 what we should expect to find in an ancestor of the modern Trype- 

 tidae. 



Family MYCETOPHILIDAE. 



ACNEMIA CYCLOSOMA, new species. 



Plate 2, fig. 4. 



Length about 5.5 mm. ; dark brown, the under side of thorax and 

 the femora yello wish- white ; wings about 5 mm. long, broad, dilute 

 brown, not spotted; hind tarsi, 3 mm. long. Antennae brown, over 

 2 mm. long, apparently 19-jointed, but the apical joints are very 

 small; the middle joints are longer than broad, cylindrical; thorax 

 almost exactly circular in lateral profile; subcosta absent or so faint 

 as to be invisible in the fossil; radius reaching costa about 1 mm. 

 before end of radial sector, the latter conspicuously and regularly 

 curved apically; costal thickening not extending beyond end of 

 radial sector; transverse (basal) section of radial sector 145 microns 

 long, and a little over 2 mm. from base of wing; media with section 

 between lower end of cross-vein to radius and fork about as long as 

 the cross- vein; cubitus simple, arched. 



Horizon and locality. — Green River Eocene ; head of East Alkali 

 Gulch, about 8 miles south of De Beque, Colorado (John P. Byram, 

 1922) . 



Holotype.—C2it. No. 69176, U.S.N.M. 



Among the Mycetophilinae, Acnemia must be considered an ad- 

 vanced or specialized genus on account of the simple cubitus. In 

 the genus Acnemia^ the present insect is in some respects more 

 specialized or modified than existing species, in spite of its antiquity. 

 According to Johannsen, in all modern species of Acnemia the costa 

 extends beyond the end of the radial sector (or should we say that the 

 sector is produced beyond its junction with the margin of the wing?), 

 but this character varies in extent. In A. fiaveola Coquillett the 

 extension is less than a fourth of the distance to the upper branch 



