GROUP OF SEA-SERPENTS, ELASMOSAUR, AND FISHES. Fishes, _Portheus_. _Elasmosaurus._ Length 50 feet. _Beryx._ _Clidastes._ Length 40 feet. _Osmeroides_, etc. _Mosasaurus._ Length 75 feet.] But the reader inquires, "What is the nature of these creatures thus left stranded a thousand miles from either ocean? How came they in the limestone of Kansas, and were they denizens of land?" These creatures lived in the Cretaceous period. The remains found in this region were mostly those of reptiles and fishes. Thirty-five species of reptiles are known from Kansas alone, representing six orders, and varying in length from ten to eighty feet. One was terrestrial, four were fliers, the rest inhabited the ocean. "When they swam over what are now the plains, the coast-line extended from Arkansas to near Fort Riley, on the Kansas River, and, passing a little eastward, traversed Minnesota to the British possessions, near the head of Lake Superior. The extent of sea to the westward was vast, and geology has not yet laid down its boundary; it was probably a shore now submerged beneath the waters of the North Pacific." Other very elongated marine reptiles of this period, but with much thicker bodies, are called, by Professor Cope, Elasmosaurs. In this group, which is not yet fully worked out, occur such genera as Cimoliosaurus, Polycotylus, Polyptychodon, and others. But it seems a pity that they should be in any way separated from the Plesiosaurs, which they strongly resemble (see chap. iv., Plate III.). Though not sea-serpents, we have introduced them here because they flourished at the same time, and lived in the same seas with the Mosasaurs and other forms of that group. The very large teeth, with strongly marked ridges, of the Polyptychodon are abundant in the Cambridge Greensand that underlies the chalk, and represent a very huge animal.