Avitelmessus

Avitelmessus grapsoideus is an extinct species of crab that lived during the Late Cretaceous. It is the only species in the genus Avitelmessus and is known from finds in the southeastern United States.

Taxonomical history
Avitelmessus was described in 1923 by Mary J. Rathbun, who assigned it to the family Atelecyclidae.[2][3] Martin Glaessner reassigned it to the family Dakoticancridae in 1960.

Description
The shell of Avitelmessus was about 2.25 inches (5.7 cm) in length and was nearly ovular in shape, with a "rounded outline".[1] The upper surface was marked by "broad, shallow grooves" which formed two attached diamond-like shapes, with the larger one closer to the front.[1] "Subsidiary" grooves came in contact with both sides of the larger diamond.[1] The "fairly blunt" anterior edge of the carapace possessed a small, central rostrum, with orbits on either side.[1] 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".[1] At least one specimen with "color markings" (considered rare among fossil crabs) has been discovered.[2] The colors are described as "a medium background, dark spots and blotches, and light lines".