What is "sigmodontes"

Sigmodont \Sig"mo*dont\, n. [Gr. ??? sigma (?) + ???, ???, a tooth.] (Zo["o]l.) Any one of a tribe ( Sigmodontes) of rodents which includes all the indigenous rats and mice of America. So called from the form of the ridges of enamel on the crowns of the worn molars. Also used adjectively.