124 KANSAS UNIVERSITY SCIENCE BULLETIN. 



tors was not able to add much to our knowledge of the gall- 

 producing stimuli. 



On the mouth parts of Hemiptera, in addition to works of a 

 general nature, I would cite two of importance in throwing 

 light upon the homopterous mouth as seen in the Psyllidse. 

 These are by Charles L. Marlatt (1898) and Walter J. Meek 

 (1903), and deal with the mouth parts of the cicada. Besides 

 these, such works as those of Sanborn on the Aphididse 

 (1905), Berlese on Coccidse (1896), and others, were of use 

 in a comparative study. The best work upon mouth parts of 

 Hemiptera is recorded in the German of Leon (1887), Geise 

 (1883), Wedde (1885), and Heymonds (1899). Dohrn (1865) 

 contributed to the internal anatomy of the Hemiptera, and 

 Witlaczil (1885) worked out the brain, eyes and digestive 

 system. 



GENERAL CHARACTERS OF THE FAMILY PSYLLID^. 



The Psyllidse were formerly classified with the Aphididse, 

 to which they are closely related, and are still sometimes 

 known as "the jumping plant lice." These insects are from 

 one-eighth to one-fifth of an inch long and in general appear- 

 ance may be likened to a minute cicada. Their principal char- 

 acters follow: Hind legs developed for jumping; antennae 

 nine- or ten-segmented (in life in constant vibration), last seg- 

 ment bearing two short spines ; tarsi two-segmented ; mouth 

 parts suctorial ; wing venation comparatively simple. Some 

 of the species are of economic interest, being injurious through 

 their feeding habits. A number form galls, notably upon 

 hackberry. A few species secrete "honey dew." 



According to Mally (1894) there are thirty-nine species and 

 varieties in North America. Only nine species are to be found 

 in the collection of the University of Kansas, four of these hav- 

 ing been taken in Kansas. So far, not many fossil insects of 

 this family are known. Scudder lists in "Tertiary Insects of 

 America" (1890) only two species, Necropsylla Hgida and 

 Catopsylla pHma, the latter being of interest, as its wing 

 venation resembles more closely that of Riley's genus Pachy- 

 psylla than of any other. 



The species taken for study belongs to this last genus, 

 Pachypsylla. The namer, C. V. Riley, says of it : "There is no 

 genus among those characterized by Dr. Fr. Low with which 



