THE GENUS PISSODES. 2*7 



they excavate transrorinatiou cells, or pupal cases, in the outer 

 portion of the wood, or, rarely, in the inner bark. These cells 

 are inclosed by a thick covering oi" excelsior-like wood fiber, form- 

 ing the so-called "chip cocoons," which are perhaps a more char- 

 acteristic feature of the species of this genus than of any other. 



GENERAL LIFE HISTORY. 



The characteristic features in the life history of the species are 

 the long life of the adult, the slow sexual maturity, the long period 

 in which eggs may be deposited by a single female, and a single 

 generation annually. In some species the broods develop within 

 two or three months after the eggs are deposited, while in others it 

 requires a longer period. The adults of some of the species emerge 

 from the bark and hibernate in the grountl, while others pass the 

 winter in the bark. 



GENERAL DISTRIBUTION. 



The genus is represented in ail sections of the United States char- 

 acterized by natural growth of their host trees, and in other sections 

 where such trees have been introduced to a sufficient extent to sup- 

 port them. (See table, pp. 40-41.) 



THE NORTH AMERICAN SPECIES OF PISSODES. 

 NATURAL CLASSIFICATION OF THE SPECIES. 



In the following key and synopses (pp. 30-38) an attempt is made 

 toward a natural classification of the species of Pissodes into primary 

 and secondary divisions, sections, series, etc., according to characters 

 which indicate lines of specialization and natural affinities. It will be 

 noted that the general modification, as in most Curculionidae, is 

 from a short or stout beak to a longer or more slender one, and in 

 general from small to larger forms. 



The characters of the pronotum, as commonly used to indicate 

 species and groups of species, are found to be of little value in sepa- 

 rating primary, or even secondary, divisions, but are of more impor- 

 tance in separating the subsections, series, and species. The special- 

 ization is plainly from a rounded, obtuse, to a rectangular and 

 acute basal angle, but this specialization is confined to the smaller 

 groups, and is therefore represented in the several sections as paral- 

 lel developments. The pronotum is, in fact, quite variable in the 

 individuals of the same species. In some reared specimens of the same 

 species there is a wide range from a rounded to an acute basal angle, 

 while in one specimen of Pissodes neinorensis the angle of one side 

 is rectangular, while that of the other is acute. These radical depar- 

 tures from the normal may, however, be considered as deformities. 



