SYSTEMATIC TREATMENT 55 



Genus PHENACOCCUS Cockerell. 



Pseudococcine forms with not less than 18 pairs of cerarii ; with a 

 denticle on the inner face of the tarsal claw ; with normally 9-segmented 

 antennae, although sometimes with 8 segments. Without a continuous 

 series of chitinized areas about the margin of the body. Male as in Pseu- 

 dococcus. Dermal pores of the triangular type present. 



Type of the genus P. aceris (Sign.). 



I have before me specimens determined by E. E. Green as P. aceris 

 (Sign.). These, together with the excellent redescription of this species 

 given by Marchal (7), permit somewhat more definite conclusions as to 

 the nature of the genus than does the original description given by Cock- 

 erell, who merely stated that the genus consists of forms with female 

 having "9-segmented antennae and secreting an ovisac." 



The presence of 18 pairs of cerarii appears to be quite constant and 

 quite characteristic of the group. In some cases the cerarii are difficult 

 to count, due to the small size of the spines, but it is usually possible to 

 determine their number with sufficient surety from the immature stages. 

 In the case of an apparently undescribed species on beech in Canada this 

 number is increased to as high as 24 by the development of what may be 

 called secondary cerarii, but I am inclined to believe that the immature 

 stages of this species would show the normal number. I consider that 

 such species as Phenacoccus man gi ferae Green cannot be regarded as 

 congeneric with P. aceris. 



The genus Tylococcus Newstead was based entirely upon the fact 

 that the cerarii in the type species are elevated upon prominent tubercles 

 and according to the original definition of this genus and the later char- 

 acterization of it by Brain, certain species included by me in Phenacoccus 

 should be referred to Tylococcus. However, I do not believe that the 

 genus is tenable on the basis of this character alone, for I have observed 

 that there is often a tendency for the cerarii to be more or less prom- 

 inent in the immature stages and in Phenacoccus artemisiae Ehrh. they 

 are borne upon very prominent tubercles which entirely disappear in the 

 adult. In the case of the undescribed species from beech, of which I have 

 spoken above, the tubercles persist in the adult female. 



The genus as I have defined it here appears to be a perfectly natural 

 group, although doubtless the examination of more species will disturb 

 this apparent harmony. Some species are included in which the specific 

 characters are extremely obscure and I anticipate that the separation of 

 any considerable series of species will be attended by much difficulty. 



