126 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



pers have been issued in a separate form, with different paging from 

 that of the volumes in which they were originally published. In such 

 cases, these separate publications will be more accessible to American 

 students than the original publications, and I have, therefore, in the 

 index used the paging as given in the separate papers instead of that 

 of the volumes. 



For the convenience of any who may not have Mr. Stainton's valuable 

 republication of Dr. Clemens's papers, I have also given references to 

 the Proceedings of the Academy of Natural Sciences, Philadelphia, and 

 those of the Entomological Society of Philadelphia, in which his papers 

 were originally published. 



It has unfortunately so happened that Professors Zeller and Frey and 

 I have been engaged in the study of the group at the same time, and 

 each to a great extent in ignorance of what the other was doing, and 

 the necessary result has been a confusion of the synonymy of some of 

 the species. This I have corrected so far as I have been able from the 

 descriptions and figures given by them ; but doubtless a comparison of 

 specimens would reveal other cases in which the same species has been 

 more than once described under different names. 



The genus OelecMa is in a chaotic condition. It includes almost any- 

 thing of a certain general type of structure. Many attempts have been 

 made to subdivide it, but, to my mind, they are all unsatisfactory. I 

 have also, myself, sometimes attempted to define new subgroups in the 

 genus, but my own efforts in this direction are not more satisfactory 

 than those of others; and while I have given them in their proper place 

 in the alphabetical arrangement, in italics, I have included all, or by far 

 the greater part of them, under Gelechia. I have pursued, also, the same 

 course with the genns Lavenia, which, though not inconveniently large, 

 Is not much better limited than Gelechia. 



By some mischance or other, I have seldom been able to look over 

 the proof-sheets of papers heretofore published by me on the Tintina, 

 scarcely a dozen proof-sheets having been examined by me. Owing to 

 this fact, and to careless writing also, no doubt the names of species 

 described or referred to by me are frequently incorrect, the same name 

 sometimes appearing under two or three different forms. 



In the following index I have attempted to correct these errors so far 

 as it may be done, and the names herein given are those that were in^ 

 tended originally in such cases. 



The imperfections of this work are many, no doubt, and are perhaps 

 more evident to me than to any one else. Nevertheless, I hope it will 

 answer sufficiently well for a present index, and for the basis of a more 

 perfect catalogue hereafter. 



Many of the generic names originally given by the authors, such as 

 Aspidisca, Blepharocera, Plicetiisa, Wilsonia, and others, are preoccupied, 

 and will have to be changed. I have not, however, made any of these 

 changes in this work, which purports to be nothing more than an 

 "index" to what has already been published. 



