Green mud differs to a greater extent from the blue mud, and owes its characteristic nature and colour to the presence of glauconite, which is formed inside the cases of foraminifera, the spines of echini and the spicules of sponges in a manner not yet understood.
Not more than 25% of the deposit may consist of bottomdwelling foraminifera, echini or worm-tubes, and as a rule these make up only from 9 to io%.
He assisted Sir Wyville Thomson in the examination and classification of the collections of the "Challenger" exploring expedition, and wrote the Review of the Echini (2 vols., 1872-1874) in the reports.
Klein (1734) to denote the tests of the Echini or sea-urchins; its later use for the animals themselves, or for the whole phylum, was an error in both history and etymology.
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