OF WASHINGTON, VOLUME XVIII, 1916 163 



uniform throughout the order that it is hard to see and more diffi- 

 cult to describe their differences in different groups. They are 

 mainly differences in length and in shape. In the Gracilariidae 

 they are like saw teeth, tapering sharply and broad at the base. 

 In some of the gelechiids they are wider in the middle. In 

 Mnemonica they look like flat plates bluntly pointed at each end. 

 That they are really flattened setae and not plates or "sensory 

 cones" is realized from a study of them in Gelechia cercericella 

 and G. gossypiella where their tubercle-like sockets are quite plain. 



Since the publication of Fr. DgGryse's paper on the "maxil- 

 lulae" we have been able to study these organs in several more 

 forms and in all where the plates are developed it is easy to iden- 

 tify genera by this character. One can place a species of Parec- 

 topa, of Gracilaria, or Ornix, or Cremastobombycia, or Ectoedemia 

 in its proper genus by the labial parts of the larva alone. In 

 Ectoedemia there are slight differences between the species but 

 they do not obscure the generic character. The maxillulae 

 however, are extremely difficult to describe in such a way as to 

 convey as accurate an idea of their structure, and for that rea- 

 son will probably not be as useful in tables or keys. To be really 

 intelligible they must be drawn. 



The ocelli are more easily handled and as Fracker observes (6) 

 offer valuable characters for the determination of genera. Occa- 

 sionally (as in Sesiidae and Tineidae) their arrangement is suffi- 

 cient to fix the family of a larva whose other body and head char- 

 acters have been obliterated; but normally they are useful more 

 as supplementary than diagnostic characters and should always 

 be considered in connection with the setae associated with them. 



The setae are after all the best guide to a study of larval origin 

 and development, showing not only the extent of separation be- 

 tween species through environment, but their affinities as well by 

 the manner in which each has reacted to the stimulus. 



BIBLIOGRAPHY. 



(1) BUSCK and BOVING: On Mnemonica auricyanea Walsingham. Proc. 



Ent. Soc. Wash., Vol. XVI, No. 4, 1914. 



(2) DAMPF A.: Zur Kenntnis Gehausetragender Lepldoptoronlarven 



Zoologischen Jahrbuchen, 1910. 



(3) DeGryse, J. J: Some Modifications of the Hypopharynx in Lepidopter- 



ous Larvae. Proc. Ent. Soc. Wash., Vol. XVII, No. 4, 1915. 



(4) DYAR, H. G. : Note on the Head Setae of Perophora melsheimerii. Jn. 



N. Y. Ent. Soc., Vol. IV, 1896. 



(5) FORBES, W. T. M. : A Structural Study of Some Caterpillars I. Ann. 



Ent. Soc. Am., Vol. Ill, No. 2, 1910. 

 FORBES, W. T. M. : 11 (The Sphingidae) Vol. IV, No. 3, 1911. 



