OCR Text |
Show 1884.] SPECIES OF OREASTER. 87 OREASTER. Species incerta. From the island of Mauritius (through M . de Robillard) came two specimens of a brick-red colour, which have at first sight a very close resemblance to 0. reticulatus ; further investigation, however, not only shows that the species are distinct from that form (though neither of them are 0. affinis), but also, and this is the curious point, striking as is their general resemblance to one another, they do not belong to the same species. Species a.-Adambulacral spinulation triplacanthid, the spines in the middle row remarkably strong, two on each plate ; superomarginal plates about 16, but only the distal plates with well-developed spines ; spines developed on the rather more numerous inferomarginals, without any marked irregularity, but they are never so long, or so strong, or so sharp as in O. reticulatus. Granules on the ventral plates coarse and large, sometimes, but rarely, forming short spines. Dorsal surface and general form not unlike that of O. reticulatus. Species j3.-Adambulacral spinulation diplacanthid, and always two outer spines for each plate : about 16 superomarginal and inferomarginal plates; the latter with fairly developed spines in the angles of the arm ; the former occasionally with small spines at the angles, but with spines only well developed quite at the distal end. The numerous spines developed among the granules of the ventral plates are not so strong, and are far less regularly arranged than in O. reticulatus. Complete accounts of these two species must be based on fuller material, and especially on specimens preserved in spirit. In addition to these two species there is yet another from Mauritius, which is represented by two badly preserved specimens ; this third species, which likewise appears to be new, has the general form of O. lincki, but has lateral rows of spines not unlike those that are found in 0. dorsatus. Just as I had come to the conclusion to issue the incomplete notices of these apparently new species, I received a copy of the first part of the 'Catalogue RaisonneV ', which I owe to the kindness of its accomplished author. In the second part of that essay, soon no doubt to be published, we shall probably obtain some more information as to these forms. OREASTER CARINATUS. Oreaster carinatus, M . Tr. p. 49. A diplacanthid form with a well-marked lophial ridge and tubercles on both series of marginal plates and on the ventral plates ; it seems to stand nearest O. productus (n. sp.), but our information with regard to it is very slight. 1 " Oatal. Raison. des Eehinodermes recueillis par M. V. de Robillard a file Maurice," par T. de Loriol (Mem. Soc. Phys. Geneve, xxviii. no. S). |