. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. 104 HISTORICAL PALEONTOLOGY. but united together in different ways into a common mass. S'ujiple corals, therefore, are the skeletons of single and inde-. I'lg. 43. — Zaphrentis Stokesi. a simple Fig-. 44.—Upper surface of a mass of "cup-coral," Upper Silurian, Canada. (After St7-o)iihodes pentagoiiiis. Upper Silurian, Billings.) Canada. (After Billings.) pendent polypes; whilst compound corals are the skeletons of assemblages or colonies of si
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. 104 HISTORICAL PALEONTOLOGY. but united together in different ways into a common mass. S'ujiple corals, therefore, are the skeletons of single and inde-. I'lg. 43. — Zaphrentis Stokesi. a simple Fig-. 44.—Upper surface of a mass of "cup-coral," Upper Silurian, Canada. (After St7-o)iihodes pentagoiiiis. Upper Silurian, Billings.) Canada. (After Billings.) pendent polypes; whilst compound corals are the skeletons of assemblages or colonies of similar polypes, living united with one another as an organic community. In the general details of their structure, the Lower Silurian Corals do not differ from the ordinary Corals of the present day. The latter, however, have the vertical calcareous plates of the coral ("septa") arranged in multiples of six or five; whereas the former have these structures arranged in multiples of four, and often showing a cross-like disposition. For this reason, the common Lower Silurian Corals are separated to form a distinct group under the name of Rugose Corals or Rugosa. They are further distinguished by the fact that the cavity of the coral (" visceral chamber ") is usually subdivided by mor^ or less numerous Ji07'izontal calcareous plates or partitions, which divide the coral into so many tiers or storeys, and which are known as the "tabulae" (fig. 45). In addition to the Rugose Corals, the Lower Silurian rocks contain a number of curious compound corals, the tubes of which have either no septa at all or merely rudimentary ones, but which have the transverse partitions or " tabulae " very highly developed. These are known as the Tabulate Corals ; and recent researches on some of their existing allies (such as Ilcliopora) liave shown that they are really allied to. Please note that these images are extracted from scanned page images that may hav
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