DIPTEEA— BIBIONID^. 585 



veins, the upper branch being connected just beyond its origin with the 

 fourth longitudinal vein, which is of the same length as the middle trans- 

 verse vein, and lies as far within as that without the middle of the wing. 

 In none of the specimens (owing to imperfect preservation) can the sixth 

 longitudinal vein be traced beyond the basal transverse vein. 



Length of body, 11"""; breadth of thorax, l.TS""; of abdomen, 1.2""; 

 length of femora: fore 3.5"", middle 3.5 (?)"", hind 3.5""; of tibia;: fore 

 3.65"", middle 3.25"", hind 4"" ; of tarsi: fore 3"", middle 2.75"", hind 3.5""; 

 of first joint of tarsi: fore 1.4"", middle 1"", hind 1.5""; length of wing, 

 10"" ; breadth of same, 3.5"°. All the measurements are taken from the 

 male. 



Similkameen River, British Columbia. Five specimens, Nos. 76, 79- 

 83 (Dr. G. M. Dawson, Geological Survey of Canada). 



Plecia pealei. 



PI. 4, Figs. 2, 3, 10, 11, 12. 



This species differs from P. similkameena mainly in a single point, the 

 earlier forking of the fourth longitudinal vein, the stalk of which is as short 

 as or shorter than the middle transverse vein, while in the British Columbia 

 species it is about twice as long. The superior fork of the third longitud- 

 inal vein is also a trifle shorter, although it does not appear to arise any 

 earlier. The cross-vein uniting the fourth longitudinal vein with the branch 

 of the fifth (next its base) is not shown in the figures, and the neuration is 

 imperfect in Figs. 2 and 3 at several points. The species is of the same 

 size as P. similkameena, but a couple of specimens, thought at first to be 

 distinct from apparent differences in their obscure neuration, but which 

 turned out to be identical on closer inspection, are somewhat smaller than 

 the average. The species must have been exceeding!}' common in the beds 

 at Twin Creek, Wyoming, for out of more than fifty specimens of fossil 

 insects obtained for me by the l)rothers Bell at their coal bed all but one 

 or two belong to this species. They are preserved in a whitish fetid shale. 

 They are mostly in a very poor state of preservation, the best of tliem 

 being shown in Figs. 2, 3, and 11, the last showing the average size. Much 

 better specimens, however, were obtained by Dr. A. C. Peale in October, 

 1877, in beds on the same creek, about thirty -five to forty miles northeast 

 of Randolph, on a darker shale, where tlie specimens were equally abundant 



