. L'histoire naturelle de Cambridge. Zoologie. Les Crinoïdes fossiles 595 point insignifiant de variation méristique comparable à la nombre variable de lignes de plaques dans les domaines de l'ancienne interradial Echinoidea ; et il est tout aussi sceptique quant à la validité d'Jaekel pour scinder le groupe en Cladocrinoidea Pentacrinoidea, et conduisant à l'avis que comme organes représentent des pinnules de totalement différent des structures dans les différents groupes. Wachsmuth et Springer adopter comme bases de classification La mesure dans laquelle les armes et leurs branches sont incorporés dans le disque, et ils reconnaissent trois divisions principales

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. The Cambridge natural history. Zoology. FOSSIL CRINOIDS 595 trifling point of meristic variation comparable to the varying number of rows of plates in the interradial areas of the older Echinoidea; and he is equally sceptical as to the validity of Jaekel's division of the group into Cladocrinoidea and Pentacrinoidea, leading to the view that organs like pinnules represent totally different structures in different groups. Wachsmuth and Springer adopt as bases of classification the extent to which the arms and their branches are incorporated in the disc, and they recognise three main divisions: Inadunata, in which the arms are completely free from the calyx; Articulata, in which the arms are partly incorporated but the tegmen remains flexible; and finally Camerata, in which the arms and their first branches are largely incorporated in the cup; the tegmen is converted into a rigid •dome and the ambu- lacral grooves on become closed, as does the mouth, by the meet- ing of overarching folds; the grooves remaining, of course, open in^the distal portions of the arms (Fig. 273). This classification, founded as it is on physiological factors, seems to the present author more satisfactory. Speaking generally, the points in which fossil Crinoids may differ from living genera are: (1) the total absence or irregular nature of the branching in the arms, so that pinnules may be said to be absent; (2) the closure of the ambulacral grooves and mouth already alluded to, and (3) the adhesion of the arms in the same ray to produce net-like structures (Crotalocrimis, Tig. 274), or a fan-shaped structure (Fetcdocrinus); (4) the frequent presence of two rows of brachials in one arm (biserial structure); (5) the develop-. if Fig. 274-—Crotalocrinuspulclier. x 1. B, basal'; Br, arm-fan of adhering branches; col, ossicle of stem; IB, infra-basal; R, radial. (After Zittel.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for re

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