136 BULLETIN 85, UNITED STATES NATIONAL MUSEUM. 



depressed from plane of A^ertex. E3'es largo, hemispherical; front 

 between and in front of lobes of vertex, "with the frons not at all, 

 or sometimes very slightly, visible around the ocellus. Antennas 

 slender, at least as long as width of head, usually much longer, 

 typically ten-segmented. Thorax broad; pronotum relatively longer 

 than in Trioza, ascending; pleural suture of pro thorax obhque, not 

 extending to middle of lateral extremity of pronotum, but to its 

 posterior edge or often not attaining to it at all. Prsescutum long. 

 Legs usually long and strong; hind tibiae often with a distinct spur 

 or tooth at base behind and with five or six black spines at apex; 

 basal tarsus of hind legs with two black, claw-like spines at apex, 

 lying one on each side of second tarsus. Forewings hyaline, trans- 

 parent, rounded at apex, never angulate; cubitus and media always 

 with a distinct petiole, which is usually distinctly shorter than the 

 basal portion of radius (discoidal subcosta) ; pterostigma nearly 

 always present; veins set with more or less visible setae, usually 

 bi-seriately. 



Type of genus. — Psylla alni Linnaeus (Chermes). 



The first use of the name Psylla was by Geoffroy * in 1762. He 

 described the genus Psylla but named no species within it, merely 

 indicating nine species by a brief Latin diagnosis. His nomenclature, 

 therefore, was binary but not binomial. This is a case exactly parallel 

 with that of Gronow's which is treated at length by the International 

 Committee on Nomenclature, and, since the generic names used in the 

 latter case are considered vaUd, there is no reason why Geoffroy's 

 Psylla should not, also, be valid. 



No species was indicated by Geoflfroy as the type-species, but in 

 1810 Latreille (1810: 264) described the genus again and made 

 Chermes alni Linnaeus the type-species. 



Lamarck (1801:298) redescribed the genus in 1801 and named 

 under it the single species Ch.Jlcus Linnaeus, but there is no evidence 

 whatever to show that he designated this as the type-species. In 

 some genera he named two or several species and before each, in every 

 case, he placed a star. He offers no explanation of the significance 

 of the star. Kirkaldy in 1904 ('04: 254) made Psylla a synonym 

 of Chermes because, he stated, Lamarck had fixed the type of the 

 latter as Chermes feus Linnaeus, which is a Psyllid and not an Aphid. 

 As a matter of fact, Lamarck does not describe Chermes at all, but, 

 as pointed out above, mentions feus under Psylla. Kirkaldy's con- 

 tention, therefore, is groundless. 



It is true that the original description of Chermes by Linnaeus fits 

 more decidedly the Psyllid group than it does Aphids or Coccids. 

 He included within it, however, species which have been subsequently 

 placed in each of these families. Geoffroy's Psylla was not, appar- 



'Histoire Abr^te des Insectes, vol. 1, 1762, p. 482. 



