30 MISCELLANEOUS FOEEST INSECTS. 



mtli P. affinis of the second division of the <2;enus Pissodes, does not 

 come within the range, but occupies the j)osition probably held by 

 the more primitive forms of the affinis division. (See Plate II.) 



MORPHOLOGICAL AND PHYSIOLOGICAL CHARACTERS AND CHARAC- 

 TERISTICS. 



The plan of combining morphological characters and physiological 

 characteristics as a basis for specific distinction, as discussed by the 

 writer in the technical contribution on Dendroctonus (Hopkins, 1909, 

 p. 64), has been followed in the study and classification of the species 

 of Pissodes. The close resemblance of the adults of allied species and 

 the wide range of specific variation render it very difficult and often 

 practically impossible to refer some of the individuals to the species 

 by external characters of the adults alone, but with information on 

 the distribution, host, habit, seasonal history, etc., they can often 

 be referred to their species without a moment's hesitation. Speci- 

 mens without locality labels and some additional information are 

 therefore of no value to the economic investigator, and will evi- 

 tlently become of less and less value to the systematists. The im- 

 portance of utilizing bionomic data as guides to the identification of 

 species will doubtless become more popular in the future and con- 

 tribute to a more rapid advancement of the essential knowledge 

 required by the systematic and economic entomologist in research 

 work. 



KEY TO THE SPECIES. 



I. Elytral interspaces 3 and 5 broader or more elevated than 2 and 4. 

 A. Elytra always with anterior and posterior spots. 



al. Elytra with distinct spots near vertex of declivity. 



bl. Beak moderately stout, always shorter than prothorax. 



cl. Elytra with distinct anterior spots and very large posterior ones- 

 Posterior spot with distinct dark border 1. similis' 



Posterior spot without distinct dark border 2. utahensis. 



c2. Elytra with indistinct anterior spots and small posterior ones. 



3. barberi. 

 h2. Beak slender, shorter or longer than prothorax. 

 c3. Elytra with anterior and posterior spots large. 



Posterior spots of elytra without dark border. Pacific Coast. 



4. sitchensis. 

 Posterior spots of elytra usually with dark border. Rocky 



Mountains 5. engelmanni. 



Posterior spots of elytra with or without dark border. Eastern 



U. S 6. strobi. 



c4. Elytra with small to moderately large anterior and posterior spots. 

 dl. Posterior brown spots moderately large. 



Posterior brown and whi te spots usually separated . East- 

 ern and northern U.S 7. approximatus. 



Posterior brown and white spots fused. Central and north- 

 ern Rocky Mountains 8. schwarzi. 



