Knefastia waltonia is an extinct species of sea snail, a marine gastropod mollusc in the family Pseudomelatomidae, the turrids and allies.

(Original description) The shell is of moderate size for the genus, fusiform, with the maximum diameter in front of the median horizontal.

The adult whorls are bicarinate, the spiral directly behind the periphery increasing in strength until it is almost or quite as elevated as the peripheral keel, from which it is separated by a rather narrow, concave interspiral area.

The area between the suture and the posterior keel is strongly concave, sculptured with 2 faint spirals, both of them introduced near the beginning of the conch, the one a little in front of the suture, the other at an equal distance behind the posterior carina, and between them a smoothly concave interspace striated with strongly and symmetrically arcuate incrementals and a few very faint spiral lirae.

[2] This extinct marine species was found in Miocene strata in the Alum Bluff Formation of Florida, USA.