(Greek κτείς Kteis) Alternatively spelled "ecteis." Literally, "comb" (of a loom), used for rake, horn, fingers, ribs, scallop, vagina, yoni.
"The Cteis was a circular and concave pedestal, or receptacle, on which the Phallus, or column [obelisk] rested. The union of these two, as the generative and producing principles of nature, in one compound figure, was the most usual mode of representation. Here we find the origin of the point within a circle, a symbol which was first adopted by the old sun worshipers. The Compass arranged above the Square symbolizes the (male) Sun, impregnating the passive (female) Earth with its life-producing rays. The true meanings, then are two-fold: the earthly (human) representations are of the man and his phallus, and the woman with her receptive cteis (vagina). The male-female divinities were commonly symbolized by the generative parts of man and woman… The Phallus and Cteis (vagina), emblems of generation and production, and which, as such, appeared in the Mysteries. The Indian Lingam was the union of both, as were the Boat and Mast, and the Point within the Circle. The Cteis was symbolized as the moon. The female personification of the productive principle. It generally accompanied the Phallus... and as a symbol of the prolific powers of nature, and was extensively venerated by the nations of antiquity." - Morals and Dogma, by Albert Pike, 
"The kteis, or female organ, as the symbol of the passive or reproductive powers of nature, generally occurs on ancient Roman monuments as the concha Veneris, a fig, barley, corn and the letter delta." - PRIAPEIA, sive diversorum poetarum in Priapum lusus, translation by Leonard C. Smithers and Sir Richard Burton