Z THE SCOLYTID BEETLES. 



Until within recent years little progress had been made toward the 

 discovery and clear definition of the specific and sexual characters. 

 In consequence the identification of the species was both difficult and 

 uncertain and has led to much confusion in both systematic and eco- 

 nomic literature. With our prasent knowledge of the genus, based 

 on an exhaustive study of the systematic and biologic details, most, 

 if not all, of the difficulties have been removed, so that the identifi- 

 cation of the species is comparatively easy. 



It is the purpose of this paper to revise and bring up to date the 

 available information on the described species, to describe those that 

 appear to be new to science, and to record the results of original inves- 

 tigations relating to the more technical details that can not well be 

 mcluded in the paper which is to follow as a part of a bulletin in the 

 regular series and which will give full information on the bionomic 

 features. 



The material which has served as a basis for the study of this genus 

 consists mainly of the notes and specimens taken by the writer in the 

 field during his connection with the West Virginia Agricultural 

 Experiment Station, between 1890 and July, 1902, including special 

 investigations for the Division of Entomology, U. S. Department of 

 Agriculture, in 1899, 1900, and 1901, and those taken during the 

 investigations by this Bureau between July, 1902, and July, 1908. 

 In addition to the large amount of material thus accumulated the 

 writer has studied the type and other specimens in the larger collec- 

 tions of this country. 



The writer desires to acknowledge, in this connection, the assist- 

 ance rendered by the following gentlemen in providing facilities for 

 the study of specimens in the collections of which they have charge : 

 Mr, Samuel Henshaw, in charge of the Le Conte collection in the 

 Museum of Comparative Zoology, Cambridge, Mass., and of the Harris 

 collection, Boston Society of Natural History; Dr. Henry Skinner, 

 in charge of the Horn collection of the American Entomological 

 Society and the general collection of the American Entomological 

 Society, Philadelphia, Pa.; Mr, E. A, Schwarz, honorary custodian of 

 Coleoptera in the Division of Insects, U, S, National Museum; Dr. 

 W. G. Dietz, who loaned type and other specimens from his collec- 

 tion, and Mr, C, O, Waterhouse, of the British Museum, who com- 

 pared specimens with the type of Dendroctonus rufipennis Kirby. 



It also gives the writer pleasure to acknowledge the efficient assist- 

 ance of Messrs, J. L. Webb, H. E. Burke, and W. F. Fiske in the field 

 and office work, of Mr, E. J. Kraus in the more recent office work, and 

 of Messrs. J. F. Strauss and R. E. Snodgrass in the preparation of the 

 illustrations for this part of the bulletin. 



