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striated exactly in a similar manner. The correspondence is indeed so 

 very close, as to render it a subject of future inquiry, whether these fos- 

 sils are not of the same species. If this question were decided in the affir- 

 mative, then would it unexpectedly turn out that the fossil, Plate VII. 

 Fig. 14, which has always hitherto been regarded as an orthoceratite, 

 is really a spirulite ; since, in another part of this slab, Fig. 19, b, an 

 oblique section is seen, of one of these fossil bodies terminating in spiral 

 convolutions. It is here proper to remark, that the spirulite in red lime- 

 stone, Plate VII. Fig. 18, also has its surface marked in a manner very 

 much resembling that of the assumed orthoceratites, Plate VII. Fig. 14. 



These fossils are far from being very abundant; nor are they very 

 generally diffused, being known, at present, to exist in very few places. 

 They are said to be found in greatest numbers in Mecklenbourg, and 

 sometimes in the neighbourhood of Francfort, where they seldom exceed 

 the ordinary belemnite in size. They are also said to be found, though 

 but rarely, in Switzerland. M. Gmelin ibund them in Siberia, and 

 M. Zukert mentions them as existing in the marble quarries of 

 Blankenbourg ; but the greatest quantities of them are discoverable in 

 the marble of Oeland, which, being of a reddish colour, and variegated 

 by the different colours of these bodies, and of the spathose matter which 

 fills their chambers, and being also susceptible of a fine polish, very 

 often yields an extremely beautiful appearance. 



Some of the pavement of Chelsea College, and of Hampton Court, 

 is paved with slabs of this, and a grey marble ; in which, when wetted, 

 numerous sections of this fossil are discoverable. The grandest specimen 

 which is, I believe, known, of this kind, is a slab, now in my possession, 

 and which originally formed a part of the museum of Mr. Strange. In 

 this specimen, a square slab of eighteen inches by thirteen, are contained 

 more than fourteen longitudinal, besides numerous transverse sections, 

 of different orthoceratites; showing, by the different directions in which 

 the sections have been formed, the various structure of the several 

 parts of these fossils. 



