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Show 1900.] MR. F. T. BEDFORD ON MALAYAN ECHINODERMS. 275 coral, sand-grains, &c, but I have obtained it on the " tangles " from mud. Distribution. The area of distribution is a somewhat anomalous one : it is fairly widely distributed over the Indo-Pacific circutn-tropical zone, extending from the Coromandel Coast on the west through the Bay of Bengal and Malay Archipelago to the Prince of Wales Is. : in the east and southwards it extends into the Antarctic littoral zone, having been found in Tasmania as well as on the South-Australian coast, but it is not reported from as far north as Hongkong or the S. Japanese seas. There seems little doubt that M . de Loriol is right in associating Studer's Schleinitzia crenularis from New Guinea with this species. Prof. Troschel and others have shown the inconstancy which the tubercles exhibit with regard to absence or presence of creuulation among recent Cidaridae; and I have followed M . de Loriol (loc. cit. 1883, p. 1) in uniting Agassiz's species of Phyllacanthus and Stephanocidaris bispinosa in Desor's genus Rhabdocidaris. The specimens brought home represent a series showing growth-changes from an individual 8 m m . in diameter to one 57 m m . in diameter. Considerable allowance has to be made for individual variations in drawing deductions from so few specimens ; but it seems worth while to give a table of the principal measurements and also to figure the changes taking place in the spines during growth. As is well known, new coronal plates are formed between the calycinals and the corona, the first-formed appearing as minute sectors between the oculars and genitals (cf. condition in Asthenosoma); and Prof. Loven has described the process of formation of the perignathic girdle and peristomal radial and interradial plates by absorption from the coronal plates and redeposition on the buccal membrane. In this species, unlike Dorocidaris papillata examined by him, the peristomal plates do not increase in number after the animal has reached a diameter of 22 mm.; and judging from the relative positions of tbe plates and spines of the corona bordering on the peristome, I conclude that no entire coronal plates have been absorbed in that region subsequent to the stage represented by the smallest of our specimens (8 m m . in diameter). The formation of new coronal plates probably continues throughout life, and the spines evidently increase in length up to a quite late stage; but whether they keep pace with the growth of tbe test is not certain, as in the largest specimen they had apparently been injured during life. W h e n first formed, tbe spines are always smooth and acquire the characteristic granulations and thorns later; but it is interesting to note that in the smaller specimens the spines acquire the typical characteristics long before they reach a length at which granulation begins to appear in the spines of larger individuals (cf. Plate X X L figs. 1 b, 1 d). In some specimens all the tubercles are smooth, while in others many of the larger tubercles are very |
