Trilobites and other crustaceans 442 " Lamp-shells and other molluscoids 193 " Common bivalve mollusks 12 " Common univalve mollusks and their allies 172 " Higher mollusks, nautili, cuttle-fishes, etc. 65 " --- In all 972 " [G] "Thesaurus Siluricus." Now in this enumeration we observe, in the first place, a representation of all the lower or invertebrate groups of the waters. We have next the remarkable fact that the Radiata of Cuvier, the lowest and most plant-like of the marine animals, are comparatively slenderly represented, yet that there are examples of their higher as well as of their lower forms. We have the further fact that the crustaceans, the highest marine animals of the annulose type, are predominant in the waters; and that in the mollusks the highest and lowest groups are most plentiful, the middle less so. The whole number of species is small, and this may arise either from our having here reached an early period in the history of life, or from our information being defective. Both are probably true. Still, of the animals known, we cannot say that the proportions of the different kinds depend on defective knowledge. There is no reason, for example, why corals should not have been preserved as well as Trilobites, or why Brachiopods should have been preserved rather then ordinary bivalves. The proportions, therefore, it may be more safe to reason from then the aggregate. In looking at these proportions, and comparing them with those of modern seas, we are struck with the great number of species representing some types either now extinct or comparatively rare: the Trilobites and Brachiopods more particularly. We are astonished at the enormous preponderance of these two groups, and especially of the Trilobites. Further, we observe that while some forms, like Lingula and Nautilus, have persisted down to modern times, others, like the Trilobites and Orthids, perished very early. In all this we can dimly perceive a fitness of living things to physical conditions, a tendency to utilise each type to the limit of its capacities for modification, and then to abandon it for something higher; a tendency of low types to appear first, but to appear in their highest perfection and variety; a sudden apparition of totally diverse plans of structure subserving similar ends simultaneously with each other, as for instance those of the Mollusk and the Crustacean; the appearance of optical and mechanical contrivances, as for example the compound eyes of the Trilobite and the swimming float of the Orthoceras, in all their perfection at first, just as they continue to this day in creatures of similar grade. That these and other similar things point to a uniform and far-reaching plan, no rational mind can doubt; and if the world had stopped short in the Primordial period,