. Bulletin of the British Museum (Natural History), Geology. . Text-fig. 5. A. Trochiliscus [EutvocMliscus) podolicus L. Devonian. Gyrogonite in median longitudinal section. xc. 55. 'B. Nitella tenuissima. Recent. Mature fruit, xc. 90. After de Bary (1871). The similarity of the layering of the lime-shell of Sycidium and Chara has already been noted by Karpinsky (1906). His pi. 3, fig. 14 shows a section of the lime-shell of a Miocene ' Chara' cut parallel to the ridges, and he observes that the spacing of the Ught and dark bands is about the same as that of the finest layers in the shel
. Bulletin of the British Museum (Natural History), Geology. . Text-fig. 5. A. Trochiliscus [EutvocMliscus) podolicus L. Devonian. Gyrogonite in median longitudinal section. xc. 55. 'B. Nitella tenuissima. Recent. Mature fruit, xc. 90. After de Bary (1871). The similarity of the layering of the lime-shell of Sycidium and Chara has already been noted by Karpinsky (1906). His pi. 3, fig. 14 shows a section of the lime-shell of a Miocene ' Chara' cut parallel to the ridges, and he observes that the spacing of the Ught and dark bands is about the same as that of the finest layers in the shell of large species of Sycidium. A few of the gyrogonites of C. hispida sectioned for this paper show a faint but definite banding in places, the bands being about 4 ju, apart, as in T. podolicus. Layering is much better shown by a gyrogonite of the fossil C. escheri (PI. 19, fig. 28), although little or no indication of layering is given by the other 50 specimens on the same slide. The dark, more or less concentric, lamellae have an average spacing of about 3 [x. The uniformity in the character and spacing of the layering in these lime-shells, allowing for the greater size of Sycidium, strongly suggests that the banding is an original feature of the lime-shell. Karpinsky (1906: 129) ascribed the growth of the lime-shell to the layering of calcium carbonate particles within a mucilaginous or gelatinous substance. Layered concretions have been produced artificially by several workers by the precipitation of salts in the presence of organic colloids (Carpenter, igoi: iioo). Through the work of Schade much light has been thrown on the principles involved and on the relations between the visible structure of concretions, their composition, and the conditions. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Britis
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