“Therefore, while there can be no doubt that _Archelon_ was strictly carnivorous in habit, and well able to navigate the open seas, it is not likely that it fed on other than relatively slow-moving prey. Lydekker looked upon the broad mandibles and broad palate of _Lytoloma_ as specializations for a mussel diet; and very similarly in _Archelon_, while the decurved beak would easily transform him into a most formidable enemy, the heavy premaxillaries and vomer, and the flat but deep lower jaw, suggest an adept crusher of crustaceans. The presence of vast quantities of _Nautilus dekayi_, which I found accompanying one of the specimens, was doubtless accidental, but it plainly suggests that this cephalopod was one of the teeming sources of food in the _Archelon_ environment. “The huge bulk of the mature _Archelon_ might account for the shearing off and loss of the flippers of younger forms caught between the shells of the ‘elder boatmen of the Cretaceous seas,’ as Cope has called them, during any sudden rush while herding on the shores. But probably the young turtles did not much frequent the shores at either egg-laying or other times. Whence it is much more likely that it was a mosasaur or some of the gigantic fishes like _Portheus_ which bit off the right hind flipper in the type-specimen of _Archelon ischyros_, well above the heel, as I have described it. That this happened rather early in life is shown by the arrested growth of the right femur and remaining portions of the tibia and fibula, which are all uniformly 10 per cent smaller than the corresponding bones of the left flipper.”