OF WASHINGTON, VOLUME XVIII, 1916 



161 



numerals. Changes in the larum itself, especially the depth of 

 the median incision, have much to do with alterations in the rela- 

 tive position of the setae, particularly those of the medial group, 

 but in spite of this a characteristic alignment prevails in certain 

 families regardless of the shape of the labrum. This is well illus- 

 trated in the Gracilariidae where the arrangement shown in Fig. 

 1 persists even through the flat stages and in spite of the most 

 radical alterations in the form of the labrum itself. The more 

 common grouping among the Micros is with M-2 laterad and 

 slightly back of M-l. 



Fig. 1 Dorsal view of a Micro Labrum (Family Gracilariidae) M-l, M-2, 

 M-S Medial setae; L-l, L-2, L-3 Lateral setae (Roman numerals show 

 Forbes' numbering of the setae). 



Fig. 2 Epipharynx of a Micro Larva; ER Epipharyngeal Rod; ES 

 Epipharyngeal Shield; ET Epipharyngeal Setae. 



Among the Micros the general alignment of the two groups is 

 at least of family significance while slight differences in propor- 

 tionate distances between setae, and differences in the relative 

 position of the individual setae are of generic value. 



Besides the dorsal setae there are two other characters of im- 

 portance on the labrum; the chitinized epipharyngeal shield in 

 the notch and three pairs of modified setae near the anterior- 

 lateral margin. The shield itself is often quite variable in dif- 

 ferent species of the same genus and only seems to be generally 

 consistent in the leaf-miners. The epipharyngeal setae are so 



