PEELIMIISrAKY CLASSIFICATION OF SCOLYTOIDEA. 175 



EPISTOMA. 



The epistoma in all of the species examined shows more or less 

 important generic and specific characters. There is a wide range of 

 modification, from a simple, transverse, chitinous piece with few or 

 no epistomal bristles to the epistomal process of Dendrodonus and 

 the exceedmgly long epistomal horn of Cadojnnus, or the flattened 

 labral-like form in Pycnarthrum. 



HYPOSTOMA. 



The hypostoma is also quite variable and can be used to good 

 advantage in the more detailed definition of a genus or larger group. 



LABRUM. 



The absence of a true labrum in the adult scolytoid beetle appears 

 to be universal. It has been stated by Eichhoff that it was present 

 in Pycnarthrum, but an examination of a balsam mount has convinced 

 the writer that this is only a produced median area of the epistoma. 



CHARACTERS IN GENERAL. 



The Body. 



The size, form, color, vestiture, sculpture, and armature of the 

 body represent characters of more or less importance in indicating 

 lines of progressive modification and as aids in generic and specific 

 definition. The size ranges from 0.4 or 0.5 mm. in the males of some 

 HyiJoiJienemus to 13 mm. in Phloeohorus. While there is more or 

 less variation in the size of the individuals of a species, the length is 

 important not only as a guide to the recognition of a species but as 

 an index to its proper position in the minor section of the genus to 

 which it belongs. The writer has found that, as a rule, the smaller 

 species of a division, subdivision, or section of a genus will, according 

 to other correlated characters, occupy a position opposite to that of 

 the larger species. In the system adopted by the writer the genera 

 with the average smaller species come first in the subfamily and in 

 each primary and minor division, and in the genus the smaller forms, 

 as a rule, precede the larger. There are, of course, exceptions to this 

 rule, especially in genera with few and widely separated species. 



FOUM. 



The form of the body ranges from elongate and slender to short and 

 stout, and it would appear that the range in progressive modification 

 is from the slender to the stouter forms. 



