The fine fossil Crab which I have now the pleasure to describe was obtained by my friend Dr. Hector, F.R.S., F.G.S., from the “passage-beds,” Ototara series, Woodpecker Bay, Brighton, north-west coast of the South Island, New Zealand, considered by him to be probably equivalent in position to the very lowest Eocene, or the uppermost Cretaceous of Europe. I have compared it with various genera of fossil Crabs with which I am acquainted, and am of opinion that its nearest alliance is with the genus Harpactocarcinus of Alphonse Milne-Edwards*, from the Nummulitic series of France, Spain, and Italy. Of this genus Alphonse Milne-Edwards has described the following six species, namely:— Of the above species the specimen from New Zealand most nearly approaches to H. quadrilobatus , Desm., in general proportions; but the carapace of the New Zealand crab is much more tumid, and the relative proportions between the depth of the anterior and posterior halves of the carapace differ considerably. Thus, if an imaginary line be drawn transversely across each carapace from the epibranchial spine on the lateral border of each, we shall find the proportions to be as under:— The carapace of the New-Zealand crab is 83 millims. broad and 73 millims. in depth from the rostrum to the posterior border. if measured along the curve of the carapace, the depth is 83 millims.; but, owing to the curvature of the carapace this is less apparent. The carapace is remarkably tumid, especially on the branchial and gastric regions; the surface of