NO. 13 STAPHYLINIDAE- — BLACKWELDER 8/ 



entire class that there is an amazing variety of divergence in the less 

 fundamental characters. The family Staphylinidae, being one of 

 the largest natural families of animals, is remarkably homogeneous 

 in general habitus and form, but presents considerable range of varia- 

 tion in many of its structures. 



In a group of this size it is to be expected that certain characters 

 which are constant in one series of species will be more variable in 

 others. This is found frequently to be the case. A certain subfamily 

 shows a regular development of a given character which thus charac- 

 terizes it, but the same character may occur scattered here and there 

 in other groups, being too variable for use in classification. 



Before any character can be safely used in classification, it is neces- 

 sary to know the extent of variation of that character throughout the 

 group being classified. If it is reasonably constant and varies only 

 in definite ways and within definite limits, then it can be safely used. 

 If, on the other hand, it be found to be very variable within small 

 groups, or to vary through a large number of slightly separated forms, 

 it can be used only with extreme care or only in certain cases. 



The range of variation in each structure or set of structures is 

 discussed in detail in the section on the comparative morphology of 

 the family. It may be seen therein that the amount of variation in 

 the numerous characters dififers very greatly. 



Characters Available for Classification 



The existing classification of the Staphylinidae, as has been pointed 

 out, is based almost entirely upon such characters as can be seen in 

 pinned specimens and with an absolute minimum of dissection, amount- 

 ing to no more than the removal of a leg to permit its examination 

 under a microscope. The study here made reveals a long series of 

 structures that may be added to the list of available characters. 



Obviously, out of the many structures to be seen on the body of 

 an insect, not all will be of aid in attempting a classification of the 

 higher groups. Some are apparently usable only for the identification 

 of species ; some appear only in small groups such as genera. Some 

 are evidently variable, and others, considered in the light of the totality 

 of structures, seem to have no phylogenetic significance. We are com- 

 pelled, then, to exercise a certain degree of judgment, based upon an 

 examination of as many species as possible, in selecting those char- 

 acters which will probably be significant as afifording bases for de- 

 fining the various categories. Out of the survey here presented the 

 following list of characters has been selected as ofi^ering probably the 

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