22 DIPTERA OF NORTH AMERICA. [PART IV. 



myia ; one submarginal cell) ; L. gracilis Zett. (probably Gonio- 

 myia; section Eriopterina ; two submarginal cells). Among 

 fourteen species, six different sections of the Tipulidde and at 

 least ten genera are represented I 



Earlier than Zetterstedt and Walker, Macquart had divided 

 Limnohia Meig. in two genera : Limnobia, with four posterior 

 cells, and LimnophUa, with five. If Mr. Zetterstedt did not 

 seem to attach any importance to the number of submarginal 

 cells, except as a specific distinction, Macquart is somewhat in 

 advance of this author ; he uses this character, but without 

 recognizing yet its full importance. His genus Limnohia is sub- 

 divided into two groups, the first of which, with a single submar- 

 ginal cell, answers to our genera Dicranomyia and Limnohia; 

 the second, with two submarginal cells, contains the species : L. 

 sylvatica M. (a LimnophUa, with four posterior cells) ; L. ^^Za- 

 typtera Macq. (the same) ; L. diana Macq. (an Eriocera), etc. 



The presence or absence of a discal cell is, in most cases, a 

 character of a very secondary value, often unreliable even for the 

 distinction of species The presence of a fifth posterior cell is 

 not always indicative of a corresponding madification in the 

 other organs. Closely allied species, in the genera Eriocera 

 and Penthoptera for instance, have a diff'erent number of posterior 

 cells. The number of submarginal cells is a character of a much 

 higher value, and can be applied with advantage to the whole 

 group of TipuUdee hrevipaljn, and not to the genus Limnobia 

 Meigen, only. But, used alone, it does not overcome the prin- 

 cipal difficulty, which consists in eliminating from the genus 

 Limnobia, in Meigeu's sense, all the foreign elements which it 

 contains. In order to attain this end, we have to use several 

 other characters. In the Froc. Acad. Nat. Sciences of Phila- 

 delphia, 1859, I have proposed a distribution, based upon the 

 number of submarginal cells, the presence or absence of spurs at 

 the tip of the tibiae, the presence or absence of empodia, the 

 structure of the ungues, the number of antennal joints, and the 

 position of the subcostal cross-vein. The scheme of this distribu- 

 tion, which is retained in the present volume, is the following : — * 



1 Instead of the names ending m formes, which I applied to the sections 

 in 1859 (Limnobiieformes, Eriopterccformes, etc.), I adopt here tlie more 

 convenient termination in ina. The name of the sixth section, Pedicica- 

 formia, is changed in Amalopina. 



I 



