Morphological Studies on the Echinoidea Holectypoida and their Allies

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Abstract
WHILE collating the plates in a recently acquired copy of the Revision of the Echini (A. Agassiz, 1872–4), I noticed with surprise a representation of complex ambulacral structure in “Echinobrissus” recens (pl. xiv a, figs. 3–4). A style of plate-grouping essentially similar to that in Echinonëus (tab. cit., figs. 7–8) is portrayed as affecting all the extra-petaloid parts of the five areas, and encroaching slightly on the distal parts of the petals. No reference to this unusual condition occurs in the text. As the proofs of my recent paper on ambulacral structures (Phil. Trans., B, vol. 209) were in my hands at the time, I was immediately impressed by the remarkable resemblance between “E.” recens and the Cretaceous Trematopygus—a correspondence by no means restricted to ambulacral plating, but involving all coronal features save the orientation of the peristome.

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