The history of the genus naming is somewhat complex. The genus was erected in 1951 by
R.V. Chamberlin based on a sample collected George Moore in Crystal-Stanislaus Cave in 1950. In 1941 Chamberlin had previously described another species that later would be moved to Sigmocheir as
Paimokia maculifer based on a single female individual. while in the second he seemingly described the same individual (based on sampling date given) along with others as
Tuolumnia dahenyi. This second citation created the synonym for the genus and confusion in later publications. The genus was finally resolved with
P. maculifer being moved to Sigmocheir and a third species,
Sigmocheir furcata, being added in 1995 by Rowland M Shelley. == Taxonomy ==