668 



PROCEEDINGS OF THE XATIOXAL MUSEUM. 



VOL. 50. 



Notes. — ^An ample series of measurements of mounted material 

 in fair condition yielded the following averages for adults of both 

 sexes : 



The relative lengths of the leg joints are as follows: Coxa, 9: 

 trochanter, 10; femur, 16; patella, 9.5; tibia, 9.5; tarsus, 10. 



Mr. Rust states that the presence of this species causes the willow 

 leaves to turn yellow and drop, but did not appear to greatly injure 

 the trees. He says that the individuals live in restricted colonies 

 under small, compact webs which almost completely conceal them. 

 These webs, according to Mr. Rust, resemble very much the webs 

 under which many true spiders deposit their eggs. No predaceous 

 species were observed in the mite colonies. 



PAH.4TETKANYCHUS PRATENSIS (Banks). 



Plate 79, fig. 16. 

 Tetranychus pratensis Banks. 1912, Proc. Wash. Eutom. Soc, vol. 14, p. 459. 



Owing, undoubtedly, to inadequate microscopic equipment, 

 Banks (14), in his original description of this species, entirely mis- 

 stated the characters of the tarsus and palpus. Recent critical 

 studies of the type material have revealed the fact that instead, as 

 Banks states, of the tarsus ending "in two long, simple, and but 

 little curved claws," it bears a single sickle-shaped claw, which gives 

 rise near its base to six appendiculate spurs. Ewing writes that 

 "the inner claw is bent downward very near its base, and beyond 

 this bend it is three-cleft." Also the palpal "thumb," in addition 

 to bearing "one stout finger and a hair at one corner," possesses the 

 usual dorsal "finger," two digituli at the upper distal corner, and 

 two short hau-s dorsally between the dorsal "finger" and base. The 

 original description as modified through the results of recent studies 

 of the type material is as follows : 



Pale greenish. Body nearly or quite twice as long as broad, 

 rather more elongate than usual, broadly rounded behind, without 

 humps above, with the usual four rows of rather long bristles, those 

 above longer than the hmd tarsi. Legs short, none as long as the 

 body, with many long hairs, some extremely long, being as long as 

 two joints together. Mandibular plate elongate, truncate, or 

 broadly rounded in front, but not emarginate. Palpal "thumb" a 



