SUBFAMILY DIASPIDINAE 229 



emarginate. Sometimes there may be two or more incisions so 

 that the lobe is divided into three or more parts. Each of these 

 subdivisions is described by some authors as a distinct lobe, they 

 are best known as lobelets and numbered in order beginning witli 

 the mesal one. The mesal lobelet, when there are only two 

 is generally larger than the lateral, if there are more than two, 

 the lateral lobelets are usually successively smaller than the 

 mesal. 



The margin of the pygidium in those species that transform 

 in a puparium or do not escape from the last nymphal exuvia, as 

 the species of the genus Aonidia, may bear a few or a considerable 

 number of lobe-like projections. These lobes are frequently 

 asymmetrically arranged and are not homologous with the lobes 

 of those species not transforming in a puparium. Such projec- 

 tions are known as pseudolobes. The development of the species 

 transforming in puparia has been so greatly accelerated, that 

 true lobes are usually not found in the pygidium of the adult fe- 

 male but in the pygidivim of the second nymphal stage and in 

 some species only in the pj^gidium of the first nymphal stage. 

 The pseudolobes are not only inconstant in different individuals 

 of the same species but may be different on the two sides of the 

 same individual. The exuviae of the second and first nymphal 

 stage of these species should be mounted for a study of the true 

 lobes and the other parts of the pygidial fringe. 



The thin projections with toothed or dentate ends located in 

 the incisurae between the lobes and upon the lateres are known 

 as pectinae. This name was given these structures by Leonardi. 

 They are also known as squamae, squames, pols, squameaux, 

 petinii, scaly hairs, notched plates, serrate plates, serrated ducts, 

 serrulate plates, fimbriate plates, fringed plates, and furcate 

 plates. The pectinae are considered as extensions of the lateral 

 margin of the pygidium. They differ from the lobes in that there 

 is always an oraceratuba located in the distal end of each. The 

 pectinae are regarded as the primitive form of these projections 

 and not the plates as is held by those who consider the plates as 

 developed from setae and the pectinae as developed in turn from 

 the plates. While there is considerable variation in the number 

 and arrangement of the pectinae, their usual disposition is two 

 in the median incisura, two or three in each second incisura, 

 usually two, and two or three in each third incisura, usually three. 

 The pectinae also vary in form, but are readily arranged in four 



