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PROP. E. W. CLAYPOLE ON HELICOPORA. 



3. On Helicopora, a new Spiral Genus (with Three Species) of 

 North-American Fenestellids. By Prof. E. W. Claypole, 

 B.A., B.Sc. (Lond.), F.G.S., of the Second Geological Survey of 

 Pennsylvania. (P„ead June 7, 1882.) 



[Plate IV.] 



The Silurian, Devonian, 'and Lower Carboniferous rocks of the 

 Mississippi basin of the United States consist of thin limestones, and 

 form altogether an insignificant mass when contrasted with the 

 enormously thick deposits of the same age on the Atlantic border in 

 Pennsylvania and the adjoining States, where the beds of corre- 

 sponding age, composed for the most part of sandstones and shales, 

 reach a thickness of from twenty to thirty thousand feet. Of 

 these western limestones the Niagara group, the equivalent of the 

 English Wenlock beds, has yielded a very rich harvest of fossil 

 remains in almost all places where its beds are well exposed ; but, 

 being a typical dolomite, its fossils almost always occur as casts, the 

 shells having been, except in very rare cases, removed by the per- 

 colation of acidulated water. 



Among the fossils of the Niagara Limestone is a great abundance 

 of fragments of various kinds of Polyzoa, especially of the family of 

 Fenestellids, but in so broken and mutilated a condition that refer- 

 ence to species is impossible. Indeed there is room for believing 

 that of the descriptions already published several may, in some cases, 

 be founded on the same species. 



During a residence of some years on the Niagara Limestone, at 

 Yellow Springs, Green Co., Ohio, I obtained, among other Polyzoa, 

 most of which were too imperfect for description, numerous speci- 

 mens of a large and striking Fenestellid, quite distinct from every 

 thing in the family already described, and yet showing features 

 that fill an existing gap, and form a connecting link between two 

 or three established genera. Before, however, proceeding with its 

 description, it will be well to review in a few words our present 

 knowledge of the American Fenestellids. 



These beautiful fossils attracted attention very early in the history 

 of palaeontology, and were known as " Lace-Corals." The first to 

 bestow on them a name was Miller of Bristol, whose name Fenestella 

 was adopted by Lonsdale in 1839. His definition, as well as those 

 of Phillips, M'Coy, and King, was more or less unsatisfactory from 

 want of precision or actual error * ; and the following definition 

 has been given by Mr. G. "W. Shrubsole, " after a careful study of 

 the several species ranging from Silurian to Carboniferous times." 



* For details, see Mr. Gr. W. Shrubsole's paper on the Carboniferous Fenes- 

 tellidse, in Q. J. Gr. S. vol. xxxvii. p. 179. 



