94 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 8T 



The second part of this study is an attempt to arrange the genera 

 in a natural order, beginning with what seem to be the least special- 

 ized. The arrangement is based on the assumptions that the closure 

 of the front coxal cavities is a high speciahzation, that the "normal" 

 antennal form is the most primitive, and that the extreme constriction 

 of the neck is more specialized. Although the genera have been 

 carefully arranged, the subgenera are not placed in any special 

 sequence. It has not been possible to examine them with suflficient 

 care to determine their iuterrelationships. This systematic list has 

 been expanded to contain a list of the species that were examined in 

 each genus and subgenus. In each case are given the original genus, 

 the genus in which it has been recently placed (if different from the 

 one to which it is herein assigned), a key to the authority for the 

 specific identification, and an indication of the habitat of the species. 

 The specimens have come from the following sources: The United 

 States National Museum (including among others the T. L. Casey 

 collection, the Hubbard and Schwarz collection, and the C. F. Baker 

 collection), the collection of the writer, and a very useful series of 

 oriental species presented by Dr. M. Cameron. The Casey collection 

 has furnished over three-fourths of the genotypes and a large part of 

 the other species included. 



The designation of genotypes in such a group as this is a very 

 important foundation for revisionary work. It must be done with 

 great care, however, especially in a group like this in which there have 

 been very few previous designations. Of the 227 names listed here, 

 19 have had genotypes designated, 127 were monobasic, and types 

 are herein designated for the remainder. 



In view of the fact that Col. T. L. Casey proposed a complete classi- 

 fication for the American Paederini (and certain others), it is neces- 

 sary to explain why his arrangement has not been satisfactory as a 

 basis for the present study. The jdrst character in Casey's key is 

 arranged as a triplet and involves the separation of those forms 

 ha\ing the prosternum reaching to the mesosternum from those 

 having it short. I have never been able to use this separation when 

 keying out species of the Medon-Lithocharis group, and I am now able 

 to state, after a careful examination of the Casey collection, that the 

 distinction either does not exist or at least does not have the impor- 

 tance that was attributed to it. The third part of the triplet does 

 mvolve a fundamental difference from the first two parts. Never- 

 theless, it seems to rne that the StUici should have been placed with 

 the first group rather than with the second, since the sternal structure 

 is a slight modification of the more generahzed type and is not similar 

 to the highly modified types of the Stilicopses, Sunii, and Echiasteres. 



Most writers have placed emphasis on the relative length of the 

 posterior tarsal subsegments and the dUation of the anterior tarsi. 



