Of the limbs, only a few bones are known, but these are very instructive. The arm bones, as shown in Fig. 84, are strikingly like those of the mosasaurs, as will be seen by comparing the figure on p. 157. The humerus is a little more elongated than that of the mosasaurs, more nearly like the mosasaurian femur. The shoulder-blade and the coracoid are imperfectly ossified, as is seen from the figure—another characteristic of aquatic life. What the fingers and toes were like cannot be said; probably they were bound together by membrane, forming swimming paddles similar to those of the mosasaurs. Some of the bones referred to the pelvis are known, but it is not known whether they are united to the spinal column by a sacrum, as in land animals. Nor is anything certainly known of the hind leg or much of the tail. Since the front legs show marked aquatic adaptations, it is altogether certain that the hind legs will be found to be modified more or less, though not so much modified as the front legs, because, as we have seen, the front legs are always more specialized in aquatic animals than the hind ones, even as the hind legs are more specialized than the front ones in land animals. Possibly the hind legs will be found to be more like those of the Thalattosuchia, as shown on p. 212, that is, partly terrestrial in character. Doubtless the tail was long and flattened, possibly with a terminal fin-like dilation, though this is less probable. As regards the habits and food of the thalattosaurs, no better summary can be given than that of Professor Merriam, in his own words: The remains of thalattosaurs are known only in purely marine deposits containing little or no material of terrestrial origin. They are associated with a fauna consisting of numerous forms, both vertebrate and invertebrate, which are not known to have existed away from marine areas. In the structure of the skeleton we find the abbreviated and broadened proximal segments of the limbs, the slender snout with prehensile terminal teeth, and the median superior nostrils, indicating a purely aquatic type. There can scarcely be room for doubt that the thalattosaurs as a group were typical marine forms. The larger and more specialized species comprised in the genus _Thalattosaurus_ were strictly natatory. They may have visited the shore, but, like the plesiosaurs, were better fitted for swimming than for crawling. Of the smaller _Nectosaurus_ we unfortunately do not know the limbs. They may have been considerably less specialized, and the animal to a correspondingly greater degree a shore-dweller. _Nectosaurus_ is, however, found in the same deposits with other forms and appears to be as common as the others; so that it is safe to consider it as having passed the greater part of its life away from the shore.