Calculus bicolor
Calculus bicolor, the sole species of the genus Calculus, is a South African spider in the family Orsolobidae. Individuals are 4 mm in length, although only juveniles have been described. The abdomen is pale yellow with a broad brown patch, and black markings on the sides of the spinnerets. Calculus bicolor was described by 1910 by William F. Purcell, and long assigned to the Oonopidae, until a 2012 study assigned Calculus to the family Orsolobidae on the basis of sensory organs that differed those of oonopids.
