l 2 THE SCOLYTID BEETLES. 
9, 10, 11, 13 to 16, and 19) Xorth American species, but none has 
been added from any other part of the world. Therefore the genus 
is now represented by 23 species from North America and one from 
Europe. 
The European species was early recognized as a destructive enemy 
of spruce and other coniferous trees, and much information has been 
published relating to its habits, life history, distribution, and methods 
of control. 
Previous to the year 1891 only two species had been recognized in 
this country as depredators on forest trees. The black turpentine 
beetle had been referred to by Olivier, 1795, and the red turpentine 
beetle by Harris, 1826 to 1862, and by other writers, as enemies of 
pine, and the eastern spruce beetle (Xo. 14), under the name of 
another species (Xo 18), was recognized as a destructive enemy 
of the spruce in the northeastern United States and southeastern 
Canada and was the subject of special investigations and reports by 
several authors. In 1891 the writer found that the southern pine 
beetle (Xo. 4) was the cause of the death of pine and spruce timber 
over extensive areas in West Virginia and adjoining States, and it 
was the subject of special investigations and reports (Hopkins, 1892 
to 1899). It was also mentioned in publications by Chittenden 
(1897), Schwarz (1898), and others. 
In 1899 the writer made observations on the destructive habits of 
the western pine beetle (Xo. 1), the red turpentine beetle (Xo. 23), 
the mountain pine beetle (Xo. 9), and the Douglas fir beetle (Xo. 
13), and observed the habits of the Sitka spruce beetle (Xo. 17). In 
1900 the destructive work of the eastern spruce beetle (Xo. 14) in 
northwestern Maine was investigated, and in 1901 investigations 
were made on the Black Hills beetle (Xo. 10) and its depredations 
in the Black Hills of South Dakota were investigated. 
Since July, 1902, many trips have been made by the writer to 
different sections of the country in general, and special investigations 
made of the work of one or more of the species of this genus, as noted 
further on, under "Basis of information/' following the account of 
each species. Messrs. J. L. Webb, H. E. Burke, and W. F. Fiske. 
assistants in forest insect investigations, working according to the 
plans and under instructions of the writer, have given special atten- 
tion to the study of the seasonal history, habits, etc., of the species 
found during their active field work. 
Mr. Webb spent two seasons (1902 and 1906) in the Black Hills 
National Forest, principally in the study of the Black Hills beetle 
(Xo. 10) and its work and in conducting experiments with trap trees: 
one season (1904) in the San Francisco National Forest, giving special 
attention to species 2, 3, and 8, and one season (1905) in central 
Idaho, studying the western pine beetle (Xo. 1) and in conducting 
