Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Ch. XXV.] FOSSILS OF THE MOUNTAIN LIMESTONE. 519 tins opinion lie is led by observing that in the existing seas the testa- cea which have colors and well-defined patterns rarely inhabit greater depths than 50 fathoms; and the greater number are found where {here is most light in very shallow water, not more than two fathoms deep. There are even examples in the British seas of testacea which are always white or color
Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Ch. XXV.] FOSSILS OF THE MOUNTAIN LIMESTONE. 519 tins opinion lie is led by observing that in the existing seas the testa- cea which have colors and well-defined patterns rarely inhabit greater depths than 50 fathoms; and the greater number are found where {here is most light in very shallow water, not more than two fathoms deep. There are even examples in the British seas of testacea which are always white or colorless when taken from below 100 fathoms; and yet individuals of the same species, if taken from shallower zones, are vividly striped or banded. This information, derived from the color of the shells, is the more welcome, because the Radiata, Articulata, and Mollusca of the Car- boniferous period belong almost entirely to genera no longer found in the living creation, and respecting the habits of which we can only hazard conjectures. Some few of the carboniferous mollusca, such as Avicula, JVucula, Solemya, and Lithodomus, belong no doubt to existing genera; but the majority, though often referred to living types, such as Isocardia, Turritella, and Buccinum, belong really to forms which appear to have become extinct at the close of the Palaeozoic epoch. Euom- phalus is a characteristic univalve shell of this period. In the inte- Fig. 576. Euomphalus pentagulatus, Sowerby. Mountain Limestone. a. Upper side. &. Lower, or umbilical side. c. View showing mouth, which is less pentagonal in older individuals, d. View of polished section, showing internal chambers. rior it is often divided into chambers (fig. 576 d), the septa or parti- tions not being perforated as in foraminiferous shells, or in those having siphuncles, like the Nautilus. The animal appears to have retreated at different periods of its growth from the internal cavity previously formed, and to have closed all commun
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