The Marine Fauna of the Mergui Archipelago. 165 



the length of the arms it is not easy to preserve specimens entire, but the 

 individual whose arms are least damaged has an arm-length of 165 mm., 

 and a disc-diameter of 17 mm. I observe that the disc of these specimens 

 shrinks considerably on being dried. 



My examples agree in every detail, except that of colour, with Lyman's 

 (1865) description of 0. cheyeni, which is synonymous with 0. hirsuta. 

 Instead of a dark prussian blue, which Lyman notes as the colour of the 

 dorsal disc-surface in alcohol, a dark brown would rather indicate the 

 prevailing colour of my specimens. 



Localities. — St. I., East of Tavoy Island and Port Owen, 4 to 12 fathoms, 

 sand and broken shells and mud (one example). St. XXIL, Hastings 

 Harbour, St Luke's Island, 3 to 20 fathoms and shore, rock and sand (two 

 examples). St. XXIII. , Five Islands, 8 to 12 fathoms, rock and sand and 

 mud (one example). St. XXIV., Cat and Kitten Islands, 8 to 22 fathoms, 

 rock and sand and broken shells (one example). St. XXV., Gregory Group 

 and Crichton Island, 4 to 14 fathoms, stones and broken shells and rock 

 (three examples). 



This species is known from Zanzibar, the Eed Sea, Mcobar, Singapore, 

 the Philippines, Fiji Islands, etc. 



(12) Ophiocampis pellucida Duncan, 1886. 



There is but a solitary example of this interesting form. 



Duncan (1886), who first described the species from material collected 

 from near King's Island, Mergui Archipelago, from which locality this 

 individual was also taken, found it possessed such unique characters that 

 he established a new genus for it. The arm bones are very peculiar. There 

 are no upper arm-plates, and the broad arched upper surface of the arm is 

 covered with a minutely squamous skin. The ventral arm-plates towards 

 the disc are almost rectangular, but farther along the arm they are distinctly 

 narrowed proximally and distally, and project at the middle. The side 

 arm-plates are large. Especially remarkable is the arrangement of the 

 opposed surfaces of the arm bones, which have a large umbo and no 

 median articulating " peg." The arms are thus not only capable of move- 

 ment in a lateral direction, but they may also, to a great degree, be curled 

 downwards. 



In my specimen the parts of the upper disc-surface seem to be con- 

 tracted or drawn together, and the radial shields, as now seen, are distinctly 

 oval in shape, and are not triangular, as in Duncan's figure. The disc- 

 diameter is 5 mm. and the arm-length is about 60 mm. While the arms 

 are buff in colour, the disc is pale yellow. 



