_Aigialosaurs._—Within recent years a number of other lizards have been made known from the Lower Cretaceous rocks of Dalmatia which present most remarkable intermediate characters between the monitors, dolichosaurs, and the mosasaurs, the famous sea-lizards of Upper Cretaceous age. Some of these lizards had twelve or thirteen vertebrae in the neck, while others had but seven—an unusually short neck characteristic of the mosasaurs. These latter kinds, belonging to two or three genera, are included in a distinct group. They were long and slender, the head long and pointed. The teeth, conical and sharp, were attached in shallow pits, quite as in the mosasaurs. The lower jaws had a hinge just back of the teeth, as in the mosasaurs, of which the only trace in modern lizards is found among the monitors. Still more remarkable, though perhaps not so easily appreciated, is the shape of the quadrate bone, with a broad flaring rim for the ear cavity, quite unlike that of land lizards, but quite like that of the mosasaurs. In fact, the very peculiar skull is almost identical with that of the true sea-lizards. The body and tail also resemble those of the mosasaurs more than those of the monitors, but there is a firm attachment of the pelvis to the backbone, and the legs are long and lizard-like, though not as long as those of land lizards. The feet were webbed in life, and the toes have no claws, conclusively demonstrating their water habits. The vertebrae indeed have the same peculiar articulations, called zygosphenes, as in most of the mosasaurs. The largest aigialosaurs were about six feet in length, that is, of about the size of the smallest known mosasaurs. [Illustration: FIG. 68.—_Clidastes_, an American mosasaur. Life restoration.] We have then in the aigialosaurs nearly every known intermediate character that we could wish for in a connecting link between the mosasaurs and the monitors, lizards that were equally at home on land or in the water, and there can be scarcely a doubt that they were either the direct ancestors or closely akin to the direct ancestors of the strictly marine mosasaurs; and scarcely a doubt that they were the descendants of the actual forbears of the modern monitors, which, as we have seen, have acquired partial aquatic habits in escaping from their enemies. The dolichosaurs we can now understand were a side branch from these semiaquatic aigialosaurs which, specializing in another direction, quickly came to grief, perhaps in competition with their more agile and skilful short-necked kin. Taking all these facts into consideration it seems best to unite the monitors, dolichosaurs, and aigialosaurs into one group of the Lacertilia, the Platynota, intermediate in place between the true land lizards and the truly aquatic mosasaurs. MOSASAURS