28 



ARKIV FÖR ZOOLOGI. BAND 8. N:0 9. 



In Cemiostoma (fig. 41) and Elachista the mandibles are of 

 Nepticula-type, with one exception: the 4th tooth is atrophied. 



This leads us över to the sap-feeders, in all of which the 

 mandibles are horizontal blades. 



The least modified of these is Ornix gattea (fig. 42) in 

 which we are still able to discern 3 distinct teeth, the external 

 one of which, however, is almost fused with the next one. 



If thus the number of teeth has grown less, the median 

 blade has increased considerably in size. The two hairs are 

 atrophied. 



In a young Gracilaria (fig. 44) the lateral tooth has dis- 

 appeared ; the two remaining ones are very long, narrow, point- 



45. 



Fig. 45. Mandible of Phyllocnistis suffusella, ventral aspect. X 386. 



ed and closely set, with finely dentate edge; the median blade 

 is very large and triangulär, slightly concave in the basal half. 



In an somewhat older larva (fig. 32) the blade is still 

 larger, with dentate edge. 



The next step has been taken by Lithocolletis (fig. 43) 

 where only one tooth remains, which, however, is large and 

 sharply pointed, with dentate inner edge. It appears that 

 the inner tooth has coalesced with the blade, except at the 



1 It is difficult to compare the number of teeth in the different forms, 

 as it is possible that secondary teeth may arise at the dorsal thin edge. 

 In the description of Gracilaria it will be noticed that I have interpreted 

 the low dorsal one as a secondary tooth, since 5 teeth seem to be typical 

 in external feeders (compare Dampf. figs. J. A 1 , H 1 ). 



