  A covariant map between the Ramond-Neveu-Schwarz (RNS) and pure spinor
formalisms for the superstring is found which transforms the RNS and pure
spinor BRST operators into each other. The key ingredient is a dynamical
twisting of the ten spin-half RNS fermions into five spin-one and five
spin-zero fermions using bosonic pure spinors that parameterize an SO(10)/U(5)
coset. The map relates massless vertex operators in the two formalisms, and
gives a new description of Ramond states which does not require spin fields. An
argument is proposed for relating the amplitude prescriptions in the two
formalisms.
