NEW OR LITTLE-KNOWN ACARI. 375 



the other (also slightly longer than the distal one). The remain- 

 ing (second) sensory hair is prone and closely applied to the 

 segment, and therefore is inconspicuous. Second tarsus with a 

 single striated sensory hair clorsally near the proximal end, and 

 it is comparatively stout. The pair of tiny oval structures 

 situated in front of the pseudostigmata are smaller and further 

 part than in P. americanus. Pseudostigmata not rounded off 

 distally (as is the case in P. spinosus and P. pilosus), but ending 

 in a point. There is only one pair of long hairs on the cephalo- 

 thorax (instead of three pairs as in P. americanus) ; each hair 

 being situated just in front of , and slightly to the side of, the 

 pseudostigmata. An exceedingly short and inconspicuous hair is 

 also present close to each of these two long hairs. The posterior 

 hair present on the cephalothorax in P. americanus is missing in 

 this species from mushrooms. Tarsus of fourth leg with quite 

 long hairs. Hairs on body long and very slightly feathered, the 

 feathering being scarcely visible even under very high magnifica- 

 tion (instead of quite distinct as in P. spinosus and P. pilosus). 



Measurements. Total length 217-297 [jl; width 100-132^. 



Habitat. Numerous specimens from off the top-surface of culti- 

 vated mushrooms ; received through the kindness of Professor H. 

 Maxwell Lefroy. 



Pygmephorus americanus Banks. (Text- fig. 15.) 



Pigmeophorus americanus Banks, Treatise on Acarina, P.U.N. 

 Mus. 1904, xxviii. p. 77, fig. 151 (figured without description). 



Pigmeophorus americanus Banks, Proc. Ent. Soc. Washington, 

 vii. p. 139 (1905). 



2 . This species is chiefly distinguished from the others of the 

 genus by the position of the little oval structures or accessory 

 stigmata * ? (situated on the cephalic segment in front of the 

 pseudostigmata), which are larger than usual and placed quite 

 close together (instead of widely apart as in P. tarsalis). Another 

 character is the shape of the pseudostigmata, which are not 

 elongated but short and globular, lacking the slight terminal 

 (apical) point present in P. tarsalis. 



Two rather long hairs are present on each side of the cephalo- 

 thorax (instead of one long hair and a very short one as in 

 P. tarsalis). There is a third pair of very long hairs on the 

 cephalothorax situated just in front of the posterior margin. 



The following details of structure may also be useful : — 



Shape of body similar to that of P. tarsalis ; some specimens 

 appear to be much wider than others (as compared with their 

 length), but this is perhaps merely clue to the pressure of the 

 cover-slip. Hairs on body distinctly plumose. First leg stouter 



* Oudemans apparently considers these minute paired oval structures to be organs 

 of sense (see Arch. Naturg. 79, Abt. A, Heft 9, p. 113, 1913), but it seems to me to 

 be more probable that they are stigmata, for they appear to be connected with the 

 respiratory trachea;. 



