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In Defence of Bothriocidaris

Published online by Cambridge University Press:  01 May 2009

Herbert L. Hawkins
Herbert L. Hawkins
Affiliation:
Professor of Geology in the University of Reading.
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Extract

Two rival hypotheses as to the origin of the Echinoidea are prevalent to-day. One of them postulates as the primitive form an organism built of a few large plates arranged in vertical series; the other demands that the earliest types should have been “scaly”, with many small plates which were regular only along the radii. Those who hold the former hypothesis see in the Ordovician Bothriocidaris a close approximation to their ideal; supporters of the latter claim that the Silurian genera Echinocystis and Palaeo1discus represent fairly well the ancestral qualities of the class. So long as Bothriocidaris is regarded as a true Echinoid, the Silurian forms lose much of their claim to be considered truly primitive; the chronological sequence is against them.

Type
Original Articles
Information
Geological Magazine , Volume 66 , Issue 2 , February 1929 , pp. 71 - 79
Copyright
Copyright © Cambridge University Press 1929

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References

page 71 note 1 In the metamorphosed Torridon sandstone of the Isle of Rum, originally composed of grains of quartz and felspar, the tridymite occurs in slender rods, tending to a radial disposition, but it is now converted to quartz.