CIMRM Supplement - Mithraeum II - rock birth. Köln, Germany.
"Colonia Agrippina/Cologne: Rock-birth from Mithraeum II, found in 1969. In this instance, most unusually, Mithras holds a bunch of wheat,ears in his l. hand, rather than a torch." (Clauss)
(Presumably in the Romisches-Germanisches Museum in Köln? RP)
The monument is described in Ristow (1974), where it is no. 24. Mentioned here in ANRW II p.2038 by Roger Beck.