OF WASHINGTON. 211 



vary in the number of joints from 3 to i, the maxillary from 4 

 to i, while the shape of the mentum, paraglossa, galea, and 

 maxilla exhibit several distinctly marked types. 



THE THORAX. 



In the second division of an insect, or the thorax, two distinctly 

 marked types of the pronotum occur, which I believe to be of 

 primary importance in classifying all insects in this order. 



In one type the pronotum does not extend back to the tegulae, 

 or the scale at the insertion of the front wings there is always a 

 small sclerite thrust in between them ; while in the other type 

 the pronotum always extends back and touches the tegulae. 



This simple character enables us to at once bring together all 

 the closely allied families in the two great sections into which 

 the Hymenoptera are divided in a way no other single character 

 will do, and it must not be overlooked by the student. 



In this connection I should like to say something of the side 

 pieces of the thorax the pleura, episterna, epimera, etc., char 

 acters found to be of primary importance in the classification of the 

 Coleoptera, and which will be found to be of the same impor 

 tance in the classification of this order ; but these characters are 

 still unanalyzed, in my mind, and while I might point out their 

 value in some particular cases, until I have satisfied myself of 

 their value in all the groups, I prefer, for the present, to say 

 nothing about them. 



With the metathorax, however, I can do better. In the meta- 

 thorax of a Hymenopterous insect are to be found some of the 

 most important characters, suitable for classification, found no 

 where else, and, strange to say, in America these important char 

 acters are entirely overlooked, or only used to a limited extent. 

 Their value and importance are not fully appreciated by us. 



We are in reality indebted to the learned Dr. Arnold Forster 

 for first calling attention to them, or, rather, making use of them, 

 in his Essay Synopsis der Familien und Gattungen der Ichneu- 

 moniden, published in 1868; but to the Swedish entomologist, 

 C. G. Thomson, for first ^really analyzing their value and mak 

 ing use of them largely in his systematic work. 



Every natural group in the Parasitica seems to have an indi- 



