SYNOPSIS OF THE NORTH AMERICAN FLIES OF THE 



GENUS SCELLUS. 



By Charles T. Greene, 

 Of the Bureau of Entomology, United States Department of Agriculture. 



INTRODUCTION. 



This synopsis is based on a large series of specimens. The location 

 of the type is designated under each species where it is known. 



I wish to acknowledge my thanks to Dr. J. M. Aldrich for his 

 criticism; to C. W. Johnson for the records which he supplied; to 

 Nathan Banks for the loan of a species from the collection of the 

 Museum of Comparative Zoology at Cambridge, Massachusetts ; and 

 to Dr. A. L. Melander who loaned me all his material of this genus. 

 Doctor Aldrich donated the type material of several species to the 

 national collection. 



HISTORICAL OUTLINE OF THE GENUS. 



The genus Scellus was established by Loew in 1857 ^ with the two 

 species Hydrophorus notatus Zetterstedt and Hydrophorus spinima- 

 nus Zetterstedt. Coquillett in 1910 - designated Hydropliorus spini- 

 jiianus Zetterstedt as type of the genus. 



The three genera Scellus, Hydrophorus, and Liancalus form a dis- 

 tinct subfamily of the Dolichopodidae and are characterized by hav- 

 ing the last section of the fifth vein shorter than the posterior cross- 

 vein, the hairs on the back of the head below forming a scattered 

 beard (instead of a ruff in a single row bordering the eye), the 

 hypopygium is directed backward or downward, not turned forward 

 under the venter. 



Liancalus is easily separated by having slender fore femora and 

 elongated fore coxae. Hydrophones and Scellus are more closely 

 related but can be easily separated. Scellus has long spines on the 

 under side of the fore femora and distinct, narrow, longitudinal 

 lines on the dorsum of the thorax. Hydrophoms has only small 

 spines on the under side of the fore femora, and the dorsum of the 

 thorax unmarked with the longitudinal lines. Sometimes there is a 

 very faint trace of these lines. 



» Neue Beitrage,, 1857, pt. 5, p. 22. 



^ Typ€-sp€cies of tJie Nortli American Diptera, Pioc. U. S. Nat. Mus., 1910, vol. 37, 

 p. 603. 



No. 2529— Proceedings U. S. National Museum, Vol. 65, Art. 16. 



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