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Growth Stages of Allagecrinus americanus Rowley

Raymond E. Peck
The Journal of Geology
Vol. 43, No. 7 (Oct. - Nov., 1935), pp. 765-770
Stable URL: http://www.jstor.org/stable/30057945
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Growth Stages of Allagecrinus americanus Rowley
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Abstract

A study of about three hundred well-preserved calyces of Allagecrinus americanus Rowley has shown an unusually complete series of growth stages. The arm facets develop first on the LAR and RPR, then on the LPR and RAR, and finally on the AR. The anal series is introduced about the same time as the facet on the AR. The orderly appearance of arm facets is accompanied by an increase in the size of the calyx, a lessening in the strength of the ornamentation, and a greater differentiation of the radial plates.

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