IV. The evolution of the cretaceous asteroidea

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Abstract
It was possible to show, in a recent monograph, that the isolated ossicles of Asteroidea, which are so frequently found by the field worker, could be identified by means of their shape and ornament. During the last four years large quantities of such material have passed through my hands. In consequence there is now sufficient evidence to trace the evolution of the great majority of Chalk Asteroidea through the whole of the zones of the chalk, and even in some cases to refer them to Jurassic ancestors. The importance of the investigation of chalk forms has been shown by Rowe (40, 41), who has pointed out (41 (v), p. 325) that “It is only in a deep-sea deposit like the Chalk, with slow, placid, and uninterrupted sedimentation taking place over vast periods of time, that we can reasonably hope to follow out every stage in the unbroken continuity of the evolution of a genus . . . .”