PKELIMIISrARY CLASSIFICATION OF SCOLYTOIDEA. 177 



males of certain species of Xylehorus, and in Am,flvicranus fastigatus 

 Blndfd. The modification of the apex appears to progress from an 

 apically serrate to a simple one or to one with an apical process. 



HEAD. 



The head is the most important part of the body in representing 

 the greatest number of taxonomic characters. Its modification is 

 from a short and narrow or broad and globular form concealed from 

 above by the pronotum, toward a narrow elongate form exposed 

 beyond the apical margin of the pronotum. The tendency toward 

 the prolonged subrostrate form indicates a line of progressive modi- 

 fication which is characteristic of the major and minor groups of all 

 of the Rhynchophora, the extremes of which are found in the smaU, 

 short, globular head of the Ipidse and the exceedingly prolonged 

 beak of Apion, Balaninus , and other genera. In the Scolytoidea, 

 Cosmoderes to Stephanoderes of the Cryphalinse have the shortest, 

 simplest head, while the extreme is reached in certain genera of the 

 Hylesininse, Hexacolinae, and Chapuisin^, with the extreme, or nearest 

 approach to Curculionidse, in Hylurgops and Hylastes. With a few 

 exceptions the concealed head is characteristic of the first division 

 of the Ipidse and the Scolytidge, while the exposed head is charac- 

 teristic of the second division of the Ipidse and the Platypodidse. 

 The antennae, eyes, and mouthparts have been discussed in pre- 

 ceding pages. The front of the head is of special importance in 

 defining the species and sexes, and ranges from convex and glabrous 

 to deeply concave and densely pubescent. 



PROTHORAX. 



The prothorax (Part I, figs. 16 and 17, pp. 23-24) represents a 

 wide range of progressive modification from long and narrow to 

 short and broad; the pronotum with sides and base not margined 

 to margined and simple or to emarginate, while the anterior dorsal 

 area ranges from closely and finely rugose to coarsely asperate, and 

 from alutaceous or opaque to smooth and shining. The pleura 

 range from convex to flat and concave, the anterior coxse fro&i con- 

 tiguous to widely separated, and the sternal, sterneUar, and post- 

 sternellar areas vary with the form of the prothorax and the size 

 and position of the coxae. The vestiture and sculpture of the an- 

 terior median and posterior dorsal and lateral areas often represent 

 generic and specific characters of special importance. 



MESOTHORAX. 



The mesothorax (Part I, figs. 18, 19) is exceedmgly variable, 

 conforming to the variable form of the body. It doubtless contains 

 many group, generic, and specific characters which may settle difficult 



