CLASSIFICATION. 17 



AleiirocMton^ Paraleyrodes^ and Udamoselis. These genera include 

 species showing a considerable variation in important characters and, 

 with other material available, furnish a basis for the consideration 

 of their ■relationships and probable lines of descent. Information 

 on these questions is essential for a correct understanding of the posi- 

 tion of the family among the Homoptera and for the assignment 

 within the family of the various species into natural groups. 



Until the recent paper by Dr. Enderlein^^ no attempt has been 

 made to divide the family into subfamilies, and to date there has been 

 no attempt to show the natural relations of the genera. Enderlein 

 erected the subfamily Udamoselinae, in which he included also 

 Aleurodicvs, and the subfamily Aleyrodinse, in which were placed all 

 other known forms. 



In the following classification we restrict Udamoselina3 to the forms 

 in which both media and cubitus are present. Our reasons for this, 

 our ideas on the relation of the genera and the systematic position of 

 the family, and a discussion of the subfamilies follow. It appears 

 to us, from a careful study of the different forms, that the Aley- 

 rodidae are not intermediate in position between the Aphididte and 

 Coccida} but that they form an offshoot from the psyllid stem. This 

 is indicated b}^ the wing venation and by the structure of the mouth- 

 parts, legs, and genitalia. 



The venation of the Avings of this family has been compared with 

 that of a psyllid wing under a separate heading (p. 9) and it is clear 

 that the ancestor of the Aleyrodidoe had a wing form and venation 

 very similar to the psjdlid type. Under another heading (pp. 12-13) 

 the genitalia of this family and those of the Psyllidse have been com- 

 pared. The resemblance here is very striking. In the males only a 

 slight modification of the structure found in the Psyllidse is necessary 

 to produce the type found in Aleurodlcus, while the Aphididie have 

 a widely different structure. In the females, too, the same condition 

 is found to be true. The ovipositors in the two families are remark- 

 ably alike, while in the Aphididac- this structure shows almost no 

 resemblance. In this second character, then, the two families are 

 thus seen to be closely related. 



The mouthparts show the most remarkable resemblance. In fact, 

 with a variation in form of some parts and a difference in size, the 

 two are identical. Even the same number of similarly formed taste 

 sensoria are present on the labium. 



In the legs, again, this similarity is to be noticed. In the presence 

 of the pulvillus and the segmentation of the tarsus, the Aleyrodidse 

 are much closer to the Psyllida? than to the Aphidida?. 



The family itself shows two distinct lines of descent. In the one 

 the media is retained, the cubitus is lost, and large compound wax 

 pores are often developed in the pupae. In the other the media is 



