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also a surface striated exactly in a similar manner. The corres- 
pondence is indeed so very close, as to render it a subject of future 
inquiry, whether these fossils are not of the same species. If this 
question were decided in the affirmative, 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 ano- 
ther 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 limestone, Plate VII. 
Fig. 18, also has its surface marked in a manner very much resem- 
bling 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 Mecklen- 
bourg, 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 found 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 spe- 
cimen 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 thir- 
teen, are contained more than fourteen longitudinal, besides numerous 
transverse sections, of different orthoceratites ; showing, by the dif- 
