PSEL APHID AE. 57 



Last joint transverse, similar to the penultimate. Ctenistes. 



Maxillary palpi with the last joint oval, with a small terminal seta. 



Tyeus. 

 Antennae with the last joint large, rounded ; 



Maxillary palpi with the third joint very small ; the fourth long, cylin- 

 drical. Cekcocekus. 

 Tarsi with a single unguis ; maxillary palpi excessively long ; 



Maxillary palpi with the last joint club-shaped. Pselaphus. 



Maxillary palpi with the last joint hatchet-shaped. Tychus. 



The anterior trochanters and thighs are armed with acute spines 

 in Ceophyllus and Cedius. Hamotus was founded by Aube on a 

 species (H. humeralis) which I cannot consider as properly sepa- 

 rated from Tyrus, and, misled by his description, I subsequently 

 described it as T. compar. The genera are all represented ih the 

 Atlantic States ; thus far only Ctenistes and Tychus have been 

 found in California. 



Group II. — Bryaxes. 



The antennas are distant at base, and inserted at the sides of 

 the head. The palpi have not the extraordinary development 

 seen in the previous group, but the last joint is oval or fusiform. 



Abdomen margined ; tarsi with a single unguis ; 



Antennas with the last three joints larger (body pubescent). Bkyaxis. 



Antennas short, with the last joint very large (body glabrous). 



Er/psENius. 

 Abdomen not margined ; ungues two, unequal. Batrisus. 



With Batrisus I have combined Arthmius Lee, described as 

 having but a single unguis ; renewed examination, with a power- 

 ful microscope, has shown me that there is a second very small 

 unguis present. The antennae are frequently very different in 

 form in the sexes of the same species of Bryaxis and Batrisus; 

 these two genera are also represented in the Pacific district. 



Tribe II.— EUPLECTINI. 



The insects of this tribe have a more depressed and linear form 

 than is seen in the preceding tribe, and approach thus to the 

 next family. The antennas are always distant, and the abdomen 

 strongly margined. The posterior coxae are conical, prominent, 

 and contiguous. The abdomen has six distinct ventral segments. 



Antenua3 geniculate ; tarsi with a single unguis. Riiexius. 



