Thus of the first order, Amorphozoa, the oolitic age produced only one genus; in the cretaceous we find thirteen genera, in the list Spongia, which is common to both. Of Zoophytes, there are twenty-three genera in the former, and seventeen in the latter—of which nine are common to both periods. The Echinodermata number eighteen in the oolite, and twenty-five in the chalk—five only common. The genus Foraminifera is entirely new in the latter formation, and consists of twelve ascertained genera, and nearly double the number of species. Of Annelida there are four genera in the oolite, and six in the chalk, in which the new order of Cirrhipeda occurs likewise. The Astacus is the only crustacean in the oolitic group: this and three new genera are found in the chalk. The Conchifera are very numerous in both deposits; forty-six in the older, and thirty-eight genera in the newer, of which eight are peculiar to the chalk. Monymaria are nearly in the same relative proportions. _Rudistes_ occurs, as a new order, for the first time in the chalk, while again the Brachiopods, Gasteropods, and Cephalopods, are about equally abundant in both formations, with additions in the chalk to the generic models. And here too the new order Pteropoda, of a single genus and species, is introduced to our contemplation. Ammonites and Belemnites do not pass this age. [Illustration: 1. Pecten quinque-costatus. 2. Plagiostoma Spinosum. 3. Hamites intermedius. 4. Spatangus cor-anguinum. 5. Galerites albogalerus. 6. Scaphites Striatus. 7. Belemnites mucronatus.] The fishes of the two periods are equally striking in their contrasts; the two orders of Ganoids and Placoids are common to both, while the Ctenoids and Cycloids appear for the first time in the history of our planet, and which were afterward to contribute so largely to the sustenance and comforts of man. The Reptilians show a declension in the latter period in numbers, with the introduction, however, of four new genera—one of which (the Iguanodon Mantelli), is also found in the wealden.