200 PROCEEDINGS OP THE ACADEMY OP 



In an appendix, I describe an interesting new genus P r o t op 1 as a, and 

 a new species ofPtychoptera Mtig. These two genera, as well as B i 1 1 a- 

 comorpha Westw., are related to each other, and seem to form a distinct 

 tribe, belonging neither to the Tipulae with short, nor to those with lougpalpi. 

 It deserves to be observed that such intermediate groups, combining the char- 

 acters of two or more larger divisions, groups small in number of species, but 

 singular and anomalous in structure, contain most of the forms which the living 

 fauna has in common with the fossil one. Thus Protoplasa is closely re- 

 lated to the fossil genus Macrochile Loew ; thus Elephantomyia 

 (among my Tipulas a n o m a 1 se) is closely allied to Toxorhina Loew, which 

 has been found living, as well as fossil; thus Rhamphidia of the same 

 group, occurs very frequently as fossil ; and it is not at all improbable, that 

 my genera A n t o c h a and Dicranoptycha will be found fossil in the 

 Prussian amber. Another circumstance worth noticing is, that so many of the 

 fossil forms, now extinct in Europe, should be found living in the New World. 

 This observation is not confined to the T i p u 1 i d ae only : Professor Loew men- 

 tions, in a recent letter to me, that he had repeated it in the Dolichopodae. It 

 is well known that similar facts have been recorded in other branches of Zoo- 

 logy, as well as in Botany. 



Many new species and even new genera remain undescribed in my collection, 

 either because I have not been able to procure a sufficient number of specimens, 

 or because I had no fresh specimens for examination. It will be noticed that at 

 the end of every description I have mentioned the number of specimens which 

 I had for comparison. The importance of this datum scarcely needs an ex- 

 planation : it is evident that the more specimens have been compared, the more 

 perfect the description ought to be ; and it is important for those who have to 

 determine specimens from descriptions, to be enabled to know how far the de- 

 scriber had the means on hand to draw a go'od description. In a very few in- 

 stances only I have ventured to describe a species from a single specimen ; and 

 that in such cases only where the characters of the species seemed striking 

 enough to secure its recognition. Another important rule to observe, is the 

 study of fresh and even living specimens. The structure of the (J 1 genital organs 

 can be studied on such specimens only; likewise, it is for the most part very 

 difficult to count the number of joints of the antennas, and to obtain a correct 

 idea of the form and the relative length of the joints of the palpi, unless from 

 living or recently killed specimens. 



Besides the number of specimens which I had for comparison, I have men- 

 tioned at the end of every description, the names of the persons from whom.1 

 have obtained them. I am exceedingly obliged in this respect for the generous 

 contributions of Mr. S. H. Scudder in Boston, Mr. A. S. Packard in Brunswick, 

 Me., Mr. Edw. Norton in Farmington, Conn., but before all to Mr. Roberf Ken- 

 nicott from Illinois, who put at my disposal highly valuable collections of Dip- 

 tera, m^de during his travels in the North Western pans of the Union. The 

 localities where I collected myself are designated by the abbreviation (nob.) 



Although nearly one hundred N. American species are known to me at pre- 

 sent, nearly all which would have been placed formerly in the old genera 

 Limnobia Meig. and Er ioptera Meig., the fauna in this respect is far 

 from being exhausted. Even now, when this paper is completed, almost every 

 ramble in the country procures me a new species, or, at least, some new fact, 

 deserving to be mentioned in the context. And if I determine upon the publi- 

 cation of this paper, it is only because I am compelled by circumstances which 

 leave me no other choice but to publish it as it is, or to give up its publication 

 altogether. 



Several European species have been found by me as occurring here and are re- 

 described under their old names. Having had no European specimens for 

 comparison, I have identified them partly from recollection, partly from existing 

 descriptions. It may happen also that among my new American species, some 



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ug. 



