THE CANADIAN ENTOMOLOGIST 203 



seen that the condition of a spHt keel-like process on the base of the inner for- 

 ceps represents almost the highest achievement in the specialization of these 

 flies. This condition is reached by E. consobrina Aleig. in Europe and by B. 

 bicarina sp. n. in America. It therefore seems certain that the split keel was 

 achieved when a land bridge connected the two great land masses. It also fol- 

 lows that the group achieved its greatest development during the period of the 

 last land bridge. Indeed, the only development of any importance that appears 

 to have taken place since the land bridge days is the reduction of the split keel 

 found in the two American species, ampelus Walk., and fissicarina sp. n. ; and 

 further studies of the palaearctic species may show^ even this slight specialization 

 to have been an ancient rather than a modern achievement. 



As there are reasons for supposing that very few, and perhaps none, of 

 the now extant species are common to the two land masses, it seems to follow 

 that although the nearctic and the palaearctic species have had a common origin 

 during the land bridge period, yet a slight further development has been 

 achieved in each of the now separated land masses during the recent period of 

 isolation. 



Synopsis of the Nearctic Species in the Genus Ernestia R. D. 



.Subgenus Meriania. 



chalybca Coq. 



flavicornis Br. 



nigrocornca sp. n. 

 Subgenus Fausta. 



No nearctic species known. 

 Subgenus Ernestia. 



frontalis sp. n. 



johnsoni sp. n. 



nigropalpis sp. n. 



arcuata sp. n. 



incisa sp. n. 



aldrichi Town. 



longicarina so. n. 



platycarina sp. n. 

 ^ sulcocarina sp. n. 



bicarina sp. n. 



ampelus Walk. 



fissicarina sp. n. 

 Subgenus Metaphyto. 



genalis Coq. 

 Key to the Subgenera of the Genus Ernestia. 



1. No discal macrochaetae on the second abdominal segment; parafacials 



hairy, at least in the females, especially on the upper part 



Subsf. Meriania 



Discal macrochaetae present on the second abdominal segment ; third an- 

 tennal segment black ; parafacials never hairy, even on the upper part 

 "...••..•• 2 



2. Width of the parafacials not nearly equal to the length of the third anten- 



