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which is common to all the shells of the trichite kind [1]. The spine being formed by protrusion, its component parts are adjusted on a different manner, and the pores like the cancelli in bones (though not so distinct) are irregular, which is the reason of its breaking obliquely in any direction, but it is generally smooth by being saturated with a plated kind of spar [2].
My ingenious and very worthy friend Mr. Brander, in a dissertation on the Belemnite, presented to the Royal Society [3], justly observes; "that the Belemnite belongs to the testaceous part of the animal kingdom, and to the family of the nautili." And I would beg leave farther to add, that this gentleman's sentiments are greatly strengthened by the surprising analogy, which the Belemnite bears to the little pearly concamerated shell, or cornu Ammonis; and the orthoceratites, to the large nautilus; the former having its siphunculus upon the verge, as the latter has it in the center of the diaphragm, or partition, of each cell or chamber. "It has indeed been truly matter of speculation (continues Mr. Brander) how this huge solid substance called the Belemnite, exclusive of the nucleas, could be formed; and how it happens, that some Belemnites should have the nucleus within them, others not; the cavity to
- ↑ Fig. 7. A piece of the Penna Marina, perforated by the Pholades.
- ↑ Spar seems to be nothing but crystal debased by a calcareous earth: the more debated fort breaks in a hairy trichite manner, the more pellucid kind with a smooth surface; and always in an oblique rhomboidal direction; which perhaps may in some measure enable us to account for its double refraction.
- ↑ Philosophical Transactions, Vol. xlviii. for 1754, page 803.
