XIV BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



mately must in many cases depend largely upon convenience, and the 

 views of those best qualified to interpret natural characters. Kot sel- 

 dom these vie^vs will rest, more or less, upon an indefinable tout ensem- 

 ble, the instinctive or natural grouping of the trained eye and mind. 

 There are no generic and specific limitations in nature; this fact, thanks 

 to modern philosophy, we have nearly all learned. But by no means 

 does it follow that there is no such thing as classification. A horse and 

 an ass might show all possible intermediate characters, so that one could 

 not say when the horse put off the caballine and took on the asinine 

 nature; but nevertheless the horse is still a horse and the ass an ass; 

 the only vexatious question would be when and where to label the one 

 cabaUus and the other asimis. So, indeed, does the question come home 

 pertinently in the small fragment of zoological life treated in the follow- 

 ing pages. With a knowledge of but few species, classification was not 

 difScult, and definition easy, but with the discovery of numerous and 

 multifarious forms generic bands become stretched and thinned till at 

 last they are rent asunder, and nothing is left but individual coherence. 

 Even a novice would be astonished at the proposition to unite a Ghryso- 

 gaster nitida and a Syr2)hits lapponicus in the same genus, yet the chain 

 between them is comi>lete : nowhere do differences exist that can be ac- 

 credited with more than specific valuation. Kor is this a solitary in- 

 instance; the majority of genera in the family do not admit of true generic 

 definition ; the best that we can do is to point out where one shall end 

 and the other begin, a proceeding which sometimes {Helophilus, for in- 

 stance) entails the result that a species differs more from some of its 

 own associates than it does from members of other genera. What, then, 

 are we to do? Make a genus for every difference? As well abandon 

 species. Make only genera that can be limited by generic characters ? 

 As well abandon the family. In steering clear of Scylla we may be 

 engulfed in Charybdis. 



No characters offer for the accurate or even clear separation into sub- 

 families. The best general division that we have was that proposed by 

 the erudite Schiner, based upon the position of the anterior cross-vein. 

 Though, like most of the higher characters in this family, it admits of 

 no sharp definition, nor dispels doubt in many cases, it is unquestion- 

 ably a natural one. In no case can a species with a well marked, oblique, 

 and exterior cross-vein be plnced among those with an internal and 

 rectangular one, yet in not a few we cannot easily decide to which of 

 the divisions a given species belongs. In the following classification 

 I have recognized fourteen groups, not because they are clearly defined, 

 for but very few are, but because some grouping is absolutely necessary. 

 It has been criticised as in some respects artificial ; this I by no means 

 deny, in the sense that they cannot be separated, except upon ulti- 

 mately trivial distinctions, but that they are in the main a natural 

 grouping I do most earnestly contend. A faunistic classification is con- 

 fesaedly imperfect, though, as in the case of Osten Sacken's Tipulidae, 



