Palaeontographical Society Monographs Volume 47, Nos. 222-225
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1893 edition. Excerpt: ...like that of the other supero-marginal plates. The abactinal area of the disk Within the boundary of the marginal plates is covered with small subregular plates or paxillar tabulae, an hexagonal form predominating. The plates in the median interradial areas are much larger than the Other Plates on the disk, and a marked diminution in size in all the plates takes place 88 they approach the margin. All the plates have their surface marked with a very fine granulation. Small entrenched pedicellariaa are occasionally present, but there appear to have been very few. _ The primary basal plates are larger than any of the other abactinal-plates. They are well seen in an example from the Upper Chalk of Kent, in which the inner side of the abactinal wall is exposed by the removal of the actinal floor and ambulacral plates. This specimen, which is preserved in the British Museum, and bears the registration number "35,496," is drawn on P1. XI, fig. 3a. The XamPl9 in question is further interesting in showing that the plates of th6 mdla-l re8'l0Ils have stellate bases, whereas the larger plates of the interradial reglons are sharply l1eXag0nal, and fit closely to their adjacent Plates (599 fig' 3 b)' _ The madreporiform body is very small, and is subsagittiform or irregularly lozenge-shaped in outline; in the example under notice it is embedded, all except l7W0 straight sides, in one large adcentrally placed basal Plate (see P1' XIV' fi8'-2d); the two straight sides are bounded each by one'lf1'/1'8'e Plate' Th: surface of the mad;-eporite is sculptured by very fine striations, which thoudg more or less wavy are directed subparallel to the adcentral sides of the b0 y. The position of the madreporite is nearer...
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