The author described a stage in the development of Comatula subsequent to the free stage of the larva, and anterior to that in which it acquires arms. He believed that the subject of the paper was of much interest in affording a key to the nature of certain aberrant forms of extinct Crinoidea, such as Haplocrinus, Stephanocrinus, &c., for the peculiarities of these genera were for the most part exhibited in the young Comatula, where they admitted of an easy determination as elements in the composition of the Crinoid.