“In any restoration of _Archelon ischyros_ only the mid-line should be accentuated as a series of rather sharp supraneural crests. These are shown to have been present by the characteristic groove-like median pits with radiating striae, which are such a prominent feature of epineurals. It is reasonable to believe that the pits mark the attachment of horny crests developed in the leathery hide. Such were doubtless projected, more or less keel-like, to a height of one or two inches, and thus gave to the mid-line of the carapace, when seen laterally, a distinctly sinuous outline not unlike that of _Toxochelys_.” As regards the habits of these ancient sea-turtles, we may offer tolerably certain conjectures. In the opinion of the writer, the less reduced plastron indicates a bottom-feeding habit, a view that is strengthened by the more rounded form of the shell, like that of the river turtle. All in all it would seem that _Protostega_ and _Archelon_ lived habitually on the soft bottoms of the shallower seas, feeding upon the hordes of large shell-fish, for which their powerful parrot-like beak was admirably adapted. That the species of _Protostega_ did not commonly frequent the deeper oceans is indicated by the general absence of their remains in the deeper water deposits. The writer, in a long collecting experience, always found their remains associated with those of the smaller _Toxochelys_, toothed birds, pterodactyls, and the smaller mosasaurs. Perhaps no one can speak more authoritatively as to the habits of these gigantic sea-turtles of the Cretaceous than Dr. Wieland: “With regard to the general habits and appearance of _Archelon_ much might doubtless be said if the present-day sea-turtles were more familiar objects. Dr. Hay thought that _Archelon ischyros_ was a clumsy or even a sluggish, mainly littoral animal, moving slowly about the bottom of quiet inlets in quest of shell-fish; I, on the contrary, much struck by the powerful flippers, and especially by the flattening of the humerus, with its low radial crest and obviously strong musculature, have held that unusual swimming power and adaptation to a strictly marine life were indicated. Perhaps, as usual where experts differ, it is probable that both views are in part correct, and that _Archelon_ was only a moderately good swimmer. It may be noted that, notwithstanding the almost circular body, the femoral notch, that for the hind leg, lies far back, so that it is not necessary, on the score of bulk, to assume slowness of motion, or the inability to pursue a sea-going life. Furthermore, it is now known that the development of the digits fell little short of that seen in _Colpochelys_ (Fig. 117) or _Eretmochelys_, truly marine turtles.