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SUMMARYThe external and internal structure of the spines of Squalus acanthias are described. Internally the spines consist of a series of dentine cones laid down one within the other. This series is reflected in the external structure by bands of pigment associated with ridges of enamel. The latter are proved to be annual.The use of the spines for age determination is discussed and the growth parameters and growth curves calculated. The results obtained differ from those of previous authors, whose work is critically discussed.

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