110 DIPTERA OF NORTH AMERICA. [PART IT. 



The habitus of the species belonging to the genus Tachytrechus 

 is very peculiar, so that they cannot be easily mistaken or con- 

 founded with species of another genus. It is difficult to give an 

 adequate expression to such peculiarities of the habitus in the 

 characteristic of a genus. All that has been said above about the 

 peculiar structure of the head, deserves in this respect especial 

 attention. A particular mark, which distinguishes the genus 

 Tachytrechus from all the other related genera is, that the face 

 reaches as far as the inferior corner of the eye. 



The species of Tachytrechus known at present are found in 

 Europe, Asia Minor, Africa and North America. 



The name of the genus (from ra^vj, rapid, and -rpf^w, I run), 

 has reference to the habit of many species to run along sandy and 

 muddy banks. 



Table for the determination of the Species. 



, f Antennae for the most part dark yellow. 1 moechus Lw. 



I Antenna; altogether black. 2 



) Tibiae brownish-yellow almost to the tip. 2 vorax Lw. 



\ Tibiae black, with a greenish reflection. 3 angustipennis Lw. 



Systematic arrangement of the Species. 

 I. The second joint of the antennae rudimentary. 



1. moechus Lw. 



II. The second joint of the antennae of the usual structure. 



2. vorax Lw. 3. angustipennis Lw. 



Description of the Species. 

 I. THE SECOND JOINT OF THE ANTENNA RUDIMENTARY. 



1. T. moechus LOEW. % and 9 Viridi-aeneus, antennis maxima 



ex parte flavis. 

 . Setae antenualis tenuissimae apice in lamellam atram dilatato, pedibus 



flavis. 

 J . Seta antennali simplice, pedibus nigro et testaceo variegatis. 



Bronze-green, antennae mostly yellow. 



. The tip of the very slender arista enlarged into a black lamella, feet 



yellow. 

 9 . Arista simple, feet partly black, partly brownish-yellow. Long. corp. 



0.240.26. Long. al. 0.220.23. 

 SYN. Tachytrechus moechus LOEW, Neue Beitr. VIII, 40, 1. 



