VI.—Growth Stages in some Jurassic Ammonites

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Abstract
Studies of the growth stages of some species of Promicroceras (Currie, 1942 and 1943) have led to similar inquiries into the growth stages of other genera. The choice of genera studied has been determined mainly by the material available; but fortunately the material available has provided an opportunity for investigation of a compressed fairly involute form (Witchellia) and some depressed involute forms (Cadoceras and some Sphaeroceratids) for comparison with the evolute Promicroceras.Most of the specimens used are from a collection of ammonites kept for study by Professor A. E. Trueman, to whom the writer is again indebted for material. Other specimens used are from the collection of the Hunterian Museum, Glasgow University. As usually happens in investigations of this kind, a number of the specimens cut had to be discarded owing to the structure being obliterated by calcification. As a result, the number of measurable sections available was smaller than one had hoped.

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