. Catalogue of the Blastoidea in the Geological Department of the British Museum (Natural History) : with an account of the morphology and systematic positionof the group, and a revision of the genera and species. British Museum (Natural History). Dept. of Geology; Blastoidea. 38 CATALOGUE OF THE BLASTOIDEA. Ophioglypha minuta (Fig. IV. C), and they together represent the deltoids of Eloea- crin us or the single calyx-inter radial of the Bolland Platycrm us. In other Ophiurids, such for example as Ophiomusium granosum and 0. validum, the interradial series starts from a basal, its lowest plate
. Catalogue of the Blastoidea in the Geological Department of the British Museum (Natural History) : with an account of the morphology and systematic positionof the group, and a revision of the genera and species. British Museum (Natural History). Dept. of Geology; Blastoidea. 38 CATALOGUE OF THE BLASTOIDEA. Ophioglypha minuta (Fig. IV. C), and they together represent the deltoids of Eloea- crin us or the single calyx-inter radial of the Bolland Platycrm us. In other Ophiurids, such for example as Ophiomusium granosum and 0. validum, the interradial series starts from a basal, its lowest plate (or plates) separating two radials (Fig. IV. D);. Diagrams to illustrate the structure of the interradial area of the calyx between the actinal and the abactinal systems. A. Elmacrinus elegans (modified from Hall). B. Platycrinus, sp. C. Ophioghjpha minuta. D. Ophiomusium validum. (C and D adapted from Lyman.) 1. Dorsocentral. 2. Under-basals. 3. Basals. 4. Radials. /. Interradials. Radial Shields. Genital Scales. 0. Orals. and a parallel to this sometimes occurs in abnormal specimens of Blastoids, such, for example, as the Pentremites sulcatus figured by Hambach1, in which two of the radials are separated by a long plate which rests on a basal below and supports the deltoid above. The posterior deltoid of Elceacrinus is divided into two parts by the anal plate; and it may be noted that the same sort of arrangement occurs in many of the earlier Palseocrinoids, in which, however, the first anal plate often rests directly on a basal, and not on a radial, as in the Blastoid. Thus, for example, Wachsmuth and Springera point out that in Glyptaster, Eucrinus, Dorycrinus, &c. "the first true interradial in the posterior area is divided, and is represented by two smaller plates, separated by a special anal ; In GJyptocrinus, which has a complete radial ring, and also five regular interradials in the first series, there is the same general arrangement of 1
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