stretched on a gallery along two sides of a large room, I could not help suggesting to him that the name of the creature should be _Teinosaurus_[AF] instead of that which he had given. Marsh has recently ascertained that the Mosasaurs were covered in part at least with bony scales. [AF] Heb. _Tanan_; Gr. _Teino_, _Tanuo_; Sansc. _Tanu_; Lat. _Tendo_.--Ges. Lex. [Illustration: LIFE IN THE MESOZOIC PERIOD. Aquatic Reptiles and Cephalopods. _Reptiles._--Plesiosaur and Osteopygis, Ichthyosaur, Teliosaur, Plesiosaur, Elasmosaur, Mosasaur (in order of the heads from left to right).--_Cephalopods._--Ammonite, Crioceras, Belemnites, Baculites, and Ammonites (in order from left to right). The Reptiles after Hawkins and Cope's Restorations.] These animals may serve as specimens of the reptilian giants of the Mesozoic seas; but before leaving them we must at least invite attention to the remarkable fact that they were contemporary with species which represent the more common aquatic reptiles of the modern world. In other words, the monsters which we have described existed over and above a far more abundant population of crocodiles and turtles then the modern waters can boast. The crocodiles were represented both in Europe and America by numerous and large species, most of them with long snouts like the modern Gavials, a few with broad heads like those of the alligators. The turtles again presented not only many species, but most of the aquatic subdivisions of the group known in modern times, as for instance the Emydes or ordinary fresh-water forms, the snapping turtles, and the soft-shelled turtles. Cope says that the Cretaceous of New Jersey alone affords twenty species, one of them a snapping turtle six feet in length. Owen records above a dozen large species from the Upper Mesozoic of England, and dates the first appearance of the turtles in England about the time of the Portland stone, or in the upper half of the Mesozoic; but footprints supposed to be those of turtles are found as far back as the Trias. Perhaps no type of modern reptiles is more curiously specialized then these animals, yet we thus find them contemporaneous with many generalized types, and entering into existence perhaps as soon as they. The turtles did not culminate in the Mesozoic, but go on to be represented by more numerous and larger species in the Tertiary and Modern. In the case of the crocodiles, while they attained perhaps a maximum toward the end of the Mesozoic, it was in a peculiar form. The crocodiles of this old time had vertebrae with a hollow at each end like the fishes, or with a projection in the front. At the end of the Mesozoic this was changed, and they assumed a better-knit back, with joints having a ball behind and a socket in front. In the Cretaceous age, species having these two kinds of backbone were contemporaneous. Perhaps this improvement in the crocodilian back had something to do with the persistence of this