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Psyche 
[Vol. 88 
one type of stridulation is produced, evidently from the linear file 
(see figure 4); the function of the fan-shaped file remains unclear. 
Although the files appear to be oriented so that they could be 
stroked from either direction, the timing of a complete palpal 
movement indicates that sound is produced only on the backstroke 
and not on the return stroke. The mechanics of stridulation by P. 
mystaceus are still incompletely understood, and need further study 
with more sophisticated filming techniques. 
Comparisons to Other Stridulatory Mechanisms 
The behavioral application of the palpi to the substrate by P. 
mystaceus differs from lycosids in that P. mystaceus moves the tips 
of the palpi while stridulating during each brief sound sequence, 
whereas the lycosids apparently remain attached in one place to the 
substrate for a prolonged sequence of sound production. The 
mechanics of sound production with the linear file are similar to 
those of the lycosids with respect to the palpus anchored by 
macrosetae and the similar file structure, but P. mystaceus differs 
from the lycosids in the location of the stridulatory organ, the type 
of movement needed to engage the file, and the reversed positions of 
the file and plectrum. Rovner (1975) proposed a new category of 
stridulatory organ (as an extension of the classification of Legendre, 
1963), type “h” to accommodate those types of mechanisms in which 
the file and plectrum (scraper) were on adjacent surfaces of a joint 
within the same appendage. I propose a subdivision of Rovner’s 
category, following Legendre’s method of subdividing categories: 
type “h I” in which the file is on the more proximal segment (as in 
lycosids), and type “h II” in which the file is on the more distal 
segment (as in P. mystaceus). 
The stridulatory mechanisms known in other spiders incorporate 
plectrum and file systems on opposing faces of the chelicerae and 
palpi, legs I and II, carapace and legs I, carapace and abdomen 
(Gertsch, 1979), or between palpal tibia and tarsus (Rovner, 1975). 
In each of these cases, either the plectrum is moved across a 
stationary file or both plectrum and file are moved together. The 
stridulatory mechanism of P. mystaceus differs from all of these in 
that the primary moving part is the file. Although the plectrum is 
passively moved in space during the movement of the palpus to 
