The Fishes of the Jurassic sea were exceedingly numerous, but were all of the Ganoid and Selachian tribes. It would weary the reader, were I to introduce here any detailed description of them, but they were as numerous and varied as those living in our present waters. There was the Hybodus, with the marked furrows on the spines and the strong hooks along their margin,--the huge Chimera, with its long whip, its curved bone over the back, and its parrot-like bill,--the Lepidotus, with its large square scales, its large head, its numerous rows of teeth, one within another, forming a powerful grinding apparatus,--the Microdon, with its round, flat body, its jaw paved with small grinding teeth,--the swift Aspidorhynchus, with its long, slender body and massive tail, enabling it to strike the water powerfully and dart forward with great rapidity. There were also a host of small Fishes, comparing with those above mentioned as our Perch, Herring, Smelts, etc., compare with our larger Fishes; but, whatever their size or form, all the Fishes of those days had the same hard scales fitting to each other by hooks, instead of the thin membranous scales overlapping each other at the edge, like the common Fishes of more modern times. The smaller Fishes, no doubt, afforded food to the larger ones, and to the aquatic Reptiles. Indeed, in parts of the intestines of the Ichthyosauri, and in their petrified excrements, have been found the scales and teeth of these smaller Fishes perfectly preserved. It is amazing that we can learn so much of the habits of life of these past creatures, and know even what was the food of animals existing countless ages before man was created. There are traces of Mammalia in the Jurassic deposits, but they were of those inferior kinds known now as Marsupials, and no complete specimens have yet been found. The Articulates were largely represented in this epoch. There were already in the vegetation a number of Gymnosperms, affording more favorable nourishment for Insects than the forests of earlier times; and we accordingly find that class in larger numbers than ever before, though still meagre in comparison with its present representation. Crustacea were numerous,--those of the Shrimp and Lobster kinds prevailing, though in some of the Lobsters we have the first advance towards the highest class of Crustacea in the expansion of the transverse diameter now so characteristic of the Crabs. Among Mollusks we have a host of gigantic Ammonites; and the naked Cephalopods, which were in later times to become the prominent representatives of that class, already begin to make their appearance. Among Radiates, some of the higher kinds of Echinoderms, the Ophiurans and Echinolds, take the place of the Crinoids, and the Acalephian Corals give way to the Astraean and Meandrina-like types, resembling the Reef-Builders of the present time. * * * * *