188-1.] specles of oreaster. *7 



Oreaster. 



Species incertce. 



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 O. 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 ; supero- 

 marginal 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 

 0. reticulatus. 



Species j3. — Adambulacral spinulation diplacanthid, and always 

 two outer spines for each plate : about 16 supermarginal 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 cpuite 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 in- 

 formation 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 " Catal. Raison. ties Eohiiiodermes recueillis par M. V. de Robillard a l'ila 

 Maurice," pur P. de Loriol (Mem. 8oc Pins. Geneve, xxviii. no. 8). 



