The
shell of
Avitelmessus was about in length and was nearly ovular in shape, with a "rounded outline". The upper surface was marked by "broad, shallow grooves" which formed two attached diamond-like shapes, with the larger one closer to the front. "Subsidiary" grooves came in contact with both sides of the larger diamond. The "fairly blunt" anterior edge of the
carapace possessed a small, central
rostrum, with
orbits on either side. The front legs were modified to become
chelipeds, with pincers formed by an upper finger, which was movable, and a lower finger, which was stationary (an extension of the previous leg segment). All limbs were covered by "fine granules". At least one specimen with "color markings" (considered rare among fossil crabs) has been discovered. The colors are described as "a medium background, dark spots and blotches, and light lines". ==Fossil sites==