INTRODUCTION. 

 Cross-veins. 



35 



a;. Humeral. 

 sex. Sabcostal. 

 icxx. Marginal, 



X*. Small, or anterior cross-vein. 

 X**. Great cross-vein. 



Other terms which have been used. 



When the veins between the end of the proefurca (i) and the 

 great cross-vein are more or less in a line, I designate them by 

 the collective terra central croi<s-veins. 



Yeins or cross-veins not found in the ordinary venation and 

 therefore not separately named, have been called supernumerary, 

 when they are of constant occurrence and distinguish a genus or 

 a species ; adventitious, when their occurrence is accidental in 

 abnormal specimens only. 



Y. Comparison of the North American and of the European 

 TiPULiD^ of the eight sections described in this volume. 



The knowledge of both faunas is far from perfect, and in this 

 country, as well as in Europe, almost every year brings with it 

 the discovery of some of the more rare and more interesting 

 forms. Only the general features of these faunas can therefore 

 be compared with a certain degree of confidence, and our state- 

 ments, with regard to the details, the numerical proportions of 

 the species, and the comparison of the smaller genera must, in a 

 certain measure, be considered as only provisional. 



What strikes us most, when we compare the number of Euro- 

 pean and North American species in the eight sections of the 

 Tipnlidae described in the present volume, is the remarkable 

 agreement, in this respect, between the two faunas. The com- 

 parison of the number of species occurring in Germany (according 

 to Dr. Schiner's enumeration), with those of the Atlantic slope 

 of this continent (as far as represented in my collection) stands 

 thus : — 



