Meristic variation in number of arm openings to the calyx of species of Dolatocrinus [Devonian] and Agaricocrinus, family Batocrinidae and other taxa of the monobathrid camerate crinoids is found to be largely infraspecific in nature, and except for isolated instances, not to be related to the size of specimens. The variants are postulated to be the result of genetic control and not of ontogenetic changes in the dorsal cup. Post-larval growth of dorsal-cup plates is judged to have been by addition of lateral and external increments to each plate, without increase in number of plates or arm openings. Similar meristic variation in number of regular interradials and of anal plates next above the primanal in the Batocrinidae is also discussed.

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