. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. 126 HISTORICAL PALAEONTOLOGY. shell is curiously subdivided in its interior by calcareous plates. The Pentameri commenced their existence at the very. Fig. 66.—Upper Silurian Polyzoa. i, Fan-shaped frond oiRhinopora I'er'nicosa; la. Portion of the surface of the same, enlarged ; 2 and ia, PJueiiopora ensiforinis, of the natural size and enlarged ; 3 and 3a, Helopora Jragilis, of the natural size and en- larged ; 4 and 4«, Ptilodictya rariporn, of the n
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. 126 HISTORICAL PALAEONTOLOGY. shell is curiously subdivided in its interior by calcareous plates. The Pentameri commenced their existence at the very. Fig. 66.—Upper Silurian Polyzoa. i, Fan-shaped frond oiRhinopora I'er'nicosa; la. Portion of the surface of the same, enlarged ; 2 and ia, PJueiiopora ensiforinis, of the natural size and enlarged ; 3 and 3a, Helopora Jragilis, of the natural size and en- larged ; 4 and 4«, Ptilodictya rariporn, of the natural size and enlarged. The speci- mens are all from the Clinton Formation (]\Iay Hill Group) of Canada. (Original.) close of the Lower Silurian (Llandovery), and survived to the close of the Upper Silurian; but they are specially character- istic of the May Hill and Wenlock groups, both in Britain and in other regions. One species, Pentamerus galeatus, is common to Sweden, Britain, and America. Amongst the remaining Upper Silurian Brachiopods are the extraordinary usually coiled into a spiral. These organs are known as the "arms," and it is from their presence that the name of ^^Brachiopoda" is derived (Gr. brachion, arm ; podes, feet). In some cases the arms are merely coiled away within the shell, without any support ; but in other cases they are carried upon a more or less elaborate shelly loop, often spoken of as the "carriage-spring ; In the Spirifei-s, and in other ancient genera, this apparatus is coiled up into a complicated spiral (fig. 67). It. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Nicholson, Henry Alleyne, 1844-1899. New York, A. L. Fowle
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Keywords: ., bookcentur, bookdecade1870, booksubjectpaleontology, bookyear1876
