Geological magazine . adually decrease and separate theorigins of two series of transversely oblong, over-lapping, lobed,bordered, and centrally punctated plates, which alternate at the sideswith a smaller row; and these are succeeded by smaller ones. • The extremity of each ray is swollen into a pyriform shape,forming an eye-protecting apparatus. The summit of this is formedby very large, convex, subglobose, punctated plates, which correspondto those at the origin of the ray. These alternate at the sides withfive very large, nearly flat, oblong, similarly ornamented plates,which articulate wi
Geological magazine . adually decrease and separate theorigins of two series of transversely oblong, over-lapping, lobed,bordered, and centrally punctated plates, which alternate at the sideswith a smaller row; and these are succeeded by smaller ones. • The extremity of each ray is swollen into a pyriform shape,forming an eye-protecting apparatus. The summit of this is formedby very large, convex, subglobose, punctated plates, which correspondto those at the origin of the ray. These alternate at the sides withfive very large, nearly flat, oblong, similarly ornamented plates,which articulate with others half their size, corresponding to theinferior row ; beneath them are others much smaller, which (withminute ossicles) border the avenue, corresponding to the under the plates of the bulbous terminations of the arms are muchlarger than those to which they correspond, except the last. The subjoined woodcut will serve to show (1) the upper and (2)under side of an arm of Oreaster hulhiferus, Forbes:—. Arm of Oreaster bulbiferus, Forbes, 1 Upper, 2 Under side, [a) ambulacra. This is one of the handsomest and most curious of all the fossilStar-fishes. It is rather rare, and seldom seen perfect. One or twoliving species of Oreaster have a similar, but not equal, developmentof plates at the extremities of the rays. The specimen figured byProfessor Forbes in Dixons Geology of Sussex is from Northfleet,, Kent; another specimen has been obtained from Sussex. The pairfigured in our Plate were obtained from the Upper Chalk ofBromley, Kent, and are preserved in the British Museum of NaturalHistory. They show the large tubercles of the dorsal surface veryclearly, and in one of them the madreporic plate (m. p.) is alsovisible. The peculiar shape of the rays is well shown in theaccompanying diagrams of their upper and under sides. The lattermay be advantageously compared with a figure given by Mr. Agassizof the same parts in the recent Pentaceros reticulatus of the NorthAm
Size: 1734px × 1442px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookidgeologicalma, bookyear1882
