OCR Text |
Show 66 PROF. F. J. BELL ON THE [Feb. 19, OREASTER NODULOSUS. Pentaceros nodulosus, Perrier, Rev. Stell. p. 237- R = 2*3 r. Disk moderately elevated, arms of moderate width, tapering gradually. The lophial and apical spines absent, and their place taken by the enlargement of the ossicles into convex rounded bodies. About 17 marginal plates in either series; it is only in the more distal regions that the inferomarginals take any share in forming the sides of the arms. Neither series are spinose. Adambulacral spinulation diplacanthid, the spines blunt; in the inner row there are ordinarily seven spines, of which the median are the more prominent ; in the outer row there are two or three larger spines, one of which is often, when only two are developed, much larger than the other ; these spines have a direction a little oblique to the longitudinal axis of the arm. Between the outer and inner rows a well-developed forcipiform pedicellaria is placed. Beyond the outer row there are irregularly shaped separate granules, which appear, at first, to afford indications of a third row of adambulacral spines. The ventral ossicles are often distinguishable from one another owing to the larger size of the granules in the centre than at the edge of the ossicle ; sessile valvular pedicellariae are richly developed among the granules. Large and coarse granules are also to be observed on the marginal plates, on which, however, pedicellariae are only rarely developed. The upper surface, both of the disk and of the arms, is delicately reticulated. The pore-areas are well separated from one another, and are, in all the more proximal parts of the arm, of some size, and contain more than twenty pores. The areas of the two lower series along the sides of the arms sometimes become fused at certain points ; the lower series extend into the space between every pair of superomarginal plates. The granulation on the nodal points is rather more delicate than on the ventral surface, and the sessile pedicellariae are exceedingly small. Nearly all the ossicles along the lophial line are enlarged ; some are more so than the rest, and two or three generally attain to considerable prominence; those which flank the apical region are large and rounded, and are, like the rest, covered with a close-set investment of rather large flat granules. A few pedicellariae are to be observed among the granules of the apical region, where no spine or protuberance of any kind is developed. The madreporite forms an elongated oval whose longer axis is directed downwards, and is placed just outside the boundary of the apical region. Colour (dry) dirty yellow, probably deep yellow in life. Measurements:- R = 53 ; r=21*5 ; breadth of arm at base 18. R = 7 0 ; r=30; breadth of arm at base 29. Hab. West Australia (Dick Hartog's Island). |