Abstract
IN the last number of the American Journal Mr. Charles Wachsmuth continues, his notes on the internal and external structure of palæozoic corals, and discusses the construction of the summit and its value in classification. He believes that while the construction of the ventral disc or actinal side of the calyx has not received the attention it deserves, it affords a clear and important distinction between recent and ancient crinoids. Commenting on Rœmer's classification of “the true crinoids which are supported by an articulated or jointed column” given in Lethœa geognostica, 1855, Mr. Wachsmuth says he expects from a dissection of Synbathocrinus that in other of the Cupressocrinidæ the central opening was closed, and that the consolidating plates were further overlaid with plates forming the floor of a passage in connection with the arm furrows and visceral cavity. In speaking of the Cyathocrinidæ he refers to the covering of Cyathocrinus, as throwing light on the summit structure of other genera, and remarks: “It is worthy of note that the Cyathocrinidæ, in the structure of their vault, bear closer resemblance to the recent crinoids than almost any other group, and seem to hold an intermediate position between modern and palæozoic types. The Cupressocrinidæ and Cyathocrinidæ thus fall naturally into a group by themselves, having the vault supported by consolidating plates and covered by an immovable arch of small plates.” In the Taxocrmidce Mr. Wachsmuth has found that there are solid plates, though they have been before described as covered by some soft material. Among the spheroidæ, which range from the Silurian to the subcarbo-niferous, the summit is found well preserved in most genera, Besides details of obsevations some generalisations are added. “Closely related as the recent crinoids are to their palæozoic ancestors in some points, the solid vault of the latter cannot in the remotest degree be homologised with the soft peristome of the former.” Many facts tend to prove that the palæozoic crinoids embracing therein all true crinoids in which the actinal side is closed, represent the young stage of growth of living types. They form a distinct group of crinoids, and it is proposed to call these paleocrinoideæ.
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American Science . Nature 16, 515–516 (1877). https://doi.org/10.1038/016515a0
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DOI: https://doi.org/10.1038/016515a0