Calculus bicolor

{{Short description|Species of spider}}

{{Speciesbox

| genus = Calculus

| species = bicolor

| parent_authority = Purcell, 1910

| authority=Purcell, 1910

}}

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.{{cite journal|last=Purcell|first= W. F.|year=1910|title= The phylogeny of the tracheae in Araneae|journal= Quarterly Journal of Microscopical Science|volume= 54|pages= 519–564|url=http://jcs.biologists.org/content/s2-54/216/519.full.pdf+html}} Calculus bicolor was described in 1910 by William F. Purcell, and long assigned to the Oonopidae (goblin spiders), until a 2012 study assigned Calculus to the family Orsolobidae on the basis of sensory organs that differed from those of oonopids.{{cite journal|last1=Platnick|first1=Norman I.|title=Tarsal organ morphology and the phylogeny of goblin spiders (Araneae, Oonopidae), with notes on basal genera.| journal=American Museum Novitates|number= 3736|year=2012|pages= 1–52|url=http://digitallibrary.amnh.org/dspace/bitstream/handle/2246/6160/N3736.pdf|display-authors=etal}}