. Ordovician fossils of north China. Paleontology; Paleontology. V<d T. Grabau—Ordovician Fossils from North Chinn (I) 59 air-chamber, first by effecting the elongation of the outer part, that which forms the new shell built by the mantle edge, and then, by the subsequent withdrawal, for a space, of the base of the reflexed part of the mantle, effecting the building of the basal layer of lime, -which is the so-called septum of the camerate portion of the Fig. 17. Hypothetical restoration of a primitive holochoaiiitic cephalopod, represented as resting with its ventral or hyp
. Ordovician fossils of north China. Paleontology; Paleontology. V<d T. Grabau—Ordovician Fossils from North Chinn (I) 59 air-chamber, first by effecting the elongation of the outer part, that which forms the new shell built by the mantle edge, and then, by the subsequent withdrawal, for a space, of the base of the reflexed part of the mantle, effecting the building of the basal layer of lime, -which is the so-called septum of the camerate portion of the Fig. 17. Hypothetical restoration of a primitive holochoaiiitic cephalopod, represented as resting with its ventral or hypononiic side upon the sea-floor, and with the shell sectioned. The stage here represented is at the beginning or the building of the camerw, previous to which it consisted only of the precamerate portion of the " siphuncle". This is here represented in section with several conical endosheaths, the spaces between which are filled with solid stereoplasm, except the median tube or " endosipho-tube ", which ends in the embryonic bulb, this being however non-calcareous and not preserved. The animal rests upon the final endosheath of the stage which surrounds the I'liilocoiic of this period. The hypothesis of camera-building by a reflexed fold of the mantle, analogous to the dorsal fold of the mantle in Xniililas, is here illustrated, the beginning ot the first camera on the dorsal side being shown. ANIMAL: a, mantle; b, marginal reflexed fold of the same, which is assumed to be functional in camera building; c, shell-muscle; d, hood; e, sipho, occupying the "endosipho-tube";/, embryonic bulb, non calcareous (when calcifield it forms the protoconch); g, hyponome; h, tentacles or arms; /, eye (left side), SHELL: ./, shell of early stage ('. e. of preseptal part of "siphuncle", (ectosiphuncle of Ruedemann); /, continuation of same into camerate state at the contraction of the "siphuncle", forming the " endosipholining " of a
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaleont, bookyear1922
