During Cretaceous times, especially in America, numerous forms of these old mesosuchian crocodiles were doubtless in existence, both slender-nosed and broad-nosed, and some of them must have been of considerable size, though none known was as large as some of the late crocodiles. This type, with biconcave vertebrae, continued to live on, in both North and South America, to the latter part of Cretaceous times, and it is even possible that some continued on into the Tertiary. But long before the close of the Cretaceous, the modern kind appeared, those with concavo-convex vertebrae, and more posterior internal nostrils. The earliest are known from New Jersey (_Thoracosaurus_, _Holops_), so like the Borneo gavials of today that they are properly classified in the same family, the Tomistomidae or Gavialidae. If all the later, procoelian type, that is, those with concavo-convex vertebrae, originated from a single form when the amphicoelian or mesosuchian type became extinct, Huxley’s classification into the Mesosuchia and Eusuchia would perhaps be proper, but we have much reason to suppose that the change in the kinds of vertebra and in the position of the nostrils was only incidental, and may have occurred in more than one line of descent, that is, it may have occurred in the broad-headed kinds of the Jurassic to the broad-headed crocodiles of today, as also in the gavial-like forms of the Cretaceous to the gavials of the present. And this is the reason why naturalists no longer recognize the classification of Huxley, which, partly perhaps because of the prestige of his name, has so long been accepted in our chief works on natural history. MARINE CROCODILES, THALATTOSUCHIA