In the next place, the animals themselves must have differed somewhat from their modern successors. This we gather from the structure of their stony cells, which present points of difference indicating corresponding difference of detail in the soft parts. Zoologists thus separate the rugose or wrinkled corals and the tabulate or floored corals of the Silurian from those of the modern seas. The former must have been more like the ordinary coral animals; the latter were very peculiar, more especially in the close union of the cells, and in the transverse floors which they were in the habit of building across these cells as they grew in height. They presented, however, all the forms of our modern corals. Some were rounded and massive in form, others delicate and branching. Some were solitary or detached, others aggregative in communities. Some had the individual animals large and probably showy, others had them of microscopic size. Perhaps the most remarkable of all is the American _Beatricea_,[H] which grew like a great trunk of a tree twenty feet or more in height, its solitary animal at the top like a pillar-saint, though no doubt more appropriate and comfortable; and multitudes of delicate and encrusting corals clinging like mosses or lichens to its sides. This creature belongs to the very middle of the Silurian, and must have lived in great depths, undisturbed by swell or breakers, and sheltering vast multitudes of other creatures in its stony colonnades. [H] First described by Mr. Billings. It has been regarded as a plant, and as a cephalopod shell; but I believe it was a coral allied to _Cystiphyllum_. [Illustration: Fig. 10.--LIFE IN THE SILURIAN AGE. On the bottom are seen, proceeding from left to right, Corals (_Stenopora_ and _Beatricea_) and a Gasteropod; _Orthoceras_; Coral (_Patria_); Crinoids, _Lingulæ_, and Cystideans; a _Trilobite_ and _Cyrtolites_. In the water is a large _Pterygotus_, and under it a _Trinucleus_. Further on, are Cephalopods, a Heteropod, and Fishes. At the surface, _Phyllograptus_, _Graptolithus_, and _Bellerophon_. On the Land, _Lepidodendron_, _Psilophyton_, and _Prototaxites_.]