EXPLANATION OF PLATES 



So far as possible the specimens chosen for iUustration have been 

 selected from collections made in the District area. In the case of 

 several species, however, no District specimens suitable for illustra- 

 tion were available. The figures of these species have been taken 

 from the best specimens procurable — usually in the author's collection 

 or the collection of the United States National Museum — regardless 

 of their place of origin. 



In the explanations of the figures all the available information 

 regarding the specimens shown is given. 



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