a row of toothed bristles on the metatarsal segment of the last leg, used to comb out cribellate silk
In spiders, the calamistrum is a row of specialized leg bristles used to comb out fine bands of silk. It is only found on cribellate spiders, that is, spiders that possess the spinning organ known as the cribellum. The calamistrum and cribellum are used to form the hackled bands of silk which are characteristic of the webs of these spiders. The ca...
• (n.) A comblike structure on the metatarsus of the hind legs of certain spiders (Ciniflonidae), used to curl certain fibers in the construction of their webs.
(from the article `spider`) ...pair having been either lost or reduced to a nonfunctional cone (colulus) or flat plate (cribellum), through which open thousands of minute ...
Cal`a·mis'trum noun [ Latin , a curling iron.] (Zoology) A comblike structure on the metatarsus of the hind legs of certain spiders ( Ciniflonidæ ), used to curl certain fibers in the construction of their webs. 
A comb-like series of hairs on metatarsus IV of cribellate spiders
The more -or less extensive row of curved hairs on the hind metatarsi, used to comb the silk from the cribellum.