The Marine Fauna of the Mergui Archipelago. 169 



The lateral arm-plates project slightly and bear arm-spines which vary 

 in number, from eight or nine next the disc to four towards the tip of the 

 arm. On the first arm-joint the lowest spine is needle-shaped, but along the 

 arm it becomes hook-shaped, and bears at first two, and then three or even 

 four, hooks all turned downwards. Close to the disc, the next three arm- 

 spines (farther along the next two or one) are broadened at the tip and 

 serrated, and each is slightly longer than the one below it. The next 

 spine, which is still a little longer, has a length of two arm-joints and is 

 the longest of all. The other spines number from four to one according 

 to the distance along the arm from the disc, and where there are two or 

 more they gradually decrease in length so that the shortest of these upper 

 spines is the most dorsal. The spines on the upper side of the longest 

 are smooth and pointed, except the one next to the longest, which for one- 

 third of the length of the arm from the disc is serrated at the tip. 



On the arm-joint next the disc, the upper five spines are united by a 

 thin translucent membrane. A similar membrane joins into a web the 

 most dorsal four spines on the second, third and fourth joints of each 

 arm. For about the next half-dozen joints there are only three spines so 

 united, and thereafter the spines are free. 



Both the dorsal and the ventral arm-plates bear fine scattered 

 granulations. There is a single flattened and pointed tentacle-scale. 



The genus Ophiopteron was founded on two specimens which Brock 

 brought from Amboina, and which Ludwig first described and figured in 

 1888, under the appropriate designation of Ophiopteron elegans. In 1894 

 Bell found seven more examples amongst the Echinodermata collected 

 from the Macclesfield Bank. Four years later, Koehler reported a single 

 example of this remarkable Ophiuroid taken by the " Investigator " from 

 the Andaman Islands. Again, in 1903, Bell reported that 0. elegans had 

 been " dredged five times in three atolls, 22 to 35 fathoms, in every case 

 near passages, hard bottom, perhaps rubble and weed," near the Maldive 

 and Laccadive Islands. It will thus ber seen how wide is the distribution 

 of this extraordinary form. 



In the reports of the "Siboga" expedition, Koehler in 1905 described two 

 other littoral species of Ophiopteron — 0. sibogae, from Lesser Sunda Island (one 

 example) ; and 0. picncto-coeruleum, from the Bay of Badjo (six examples), 

 from the Aru Islands (one example), and from the Island of Botti (one 

 example). 



A fourth species has now been discovered among the Echinodermata 

 collected in the Mergui Archipelago. It is, unfortunately, represented by a 

 single example, which, however, is fairly well preserved. It is extremely 



