The Marine Fauna of the Mergui Archipelago. 159 



The dorsal arm-plates are distinctly arched. The innermost plate at the 

 base of the radial shields is triangular, the second is roughly square, the third 

 is rectangular and slightly broader than long. From the fourth outwards to 

 the tip of the arm, the plates are longer than broad, and are four- sided with a 

 narrow proximal edge, two straight outward sloping lateral edges, and a wide 

 curved distal edge. 



A very marked feature of the arms of my specimens is their variegation, 

 brownish coloured rings occurring at about every fourth articulation. 



Outside the area of the disc there is but one tentacle-scale. 



Measurement gives ratio of arm-length to disc-diameter to be fully 3 : 1, 

 and my specimens vary from over 5 to just under 9 mm. in diameter. 



Localities. — Four specimens from St. I., east of Tavoy Island and Port 

 Owen, 4 to 12 fathoms, sand and broken shells and mud. St. XIIL, Shore of 

 Maria Island, 8 to 10 fathoms, rock and sand (one specimen). St. XIV., 

 Bushby Island pearling ground, shore to 21 fathoms, sand and mud (one speci- 

 men). St. XXII., Hastings Harbour, St. Luke's Island, shore to 20 fathoms, 

 rock and sand (one specimen). St. XXV., Gregory Group and Crichton 

 Island, 4 to 14 fathoms, stones and broken shells and rock (four examples). 



0. sinensis has been recorded by Lyman from the neighbourhood of Yoko- 

 hama, and by Koehler from the Malabar coast, from the south of Ceylon and 

 round the Bay of Bengal. It has also been found (Koehler) near the Andaman 

 Islands, and in the Mergui Archipelago (King's Island). It appears to be a 

 littoral form, having been taken in these places at a depth of from 4 to 36 

 fathoms. 



(3) Ophiactis savignyi Miiller et Troschel. 



A single small and somewhat damaged example is the only representative 

 of this species. 



Much has been written by Lyman, Grube, Ludwig, De Loriol, Koehler and 

 others, on the synonymy of Ophiactis savignyi, 0. sexradia, 0. reinhardti, 0. 

 incisa, 0. virescens and 0. krebsii. All that need be added is that if one 

 species, 0. savignyi, is to include all these forms, there are undoubtedly great 

 variations amongst the individuals of that species. 



My solitary example has a disc-diameter of 4 mm. and an arm-length of 

 15 mm. It is the form with five arms, each arm carrying six short and stout 

 arm-spines, one tentacle-scale, ventral arm-plates longer than they are broad, 

 the disc without spines, and the radial shields non-diverging, and the length 

 of each about two-thirds the radius of the disc. 



Locality. — St. XX., Hastings Harbour, St. Luke's Island, 3 to 20 fathoms 

 and shore, rock and sand (one example). 



