Source : Webster's Revised Unabridged Dictionary (1913)

Calamistrum \Cal`a*mis"trum\, n. [L., a curling iron.]
   (Zo["o]l.)
   A comblike structure on the metatarsus of the hind legs of
   certain spiders ({Ciniflonid[ae]}), used to curl certain
   fibers in the construction of their webs.