192 PERCY SLADEN TRUST EXPEDITION 



TRACHOMEDgSJC. 



28. Olindias singularis, Browne, 1904. 



Olindias singularis, Browne, 1904, p. 737, pi. 56, fig. 2, pi. 57, fig. 1. 



Olindias singularis, Bigelow, 1909, p. 109, pi. 4, fig. 1, pi. 31, figs. 1 — 10, pi. 32, fig. 8. 



Olindias singularis, Mayer, 1910, p. 357. 



Locality. Ohagos Archipelago, Diego Garcia. 10 — 14 fms. 10 July, 1905. 

 4 specimens. 



This species was first described by me from a single specimen, which Professor Stanley 

 Gardiner found on his expedition to the Maldive Archipelago. 



The chief specific character was based upon the presence of a single sense organ at 

 the base of the primary tentacles. All the other species of the genus having a pair of 

 sense organs in that position. 



Bigelow fortunately found no less than 23 specimens in Managreva Harbour, 

 Paumotu Archipelago in the Tropical Pacific, and he has given, a more adequate 

 description of the species, accompanied by excellent figures. In that series of specimens 

 Bigelow noticed that the presence of a single sense organ did not hold good, for in the 

 largest specimens (30 — 60 mm. in diameter) single and paired sense organs were found 

 in the proportion of about four to one. 



On searching the margin of the umbrella of the specimens from Diego Garcia I could 

 find only a single sense organ at the base of the primary tentacles in three specimens, 

 but the fourth specimen showed the presence of pairs. In quadrant (A) thirteen singles 

 occurred, in quadrant (B) twenty-three singles and two pairs, in quadrant (C) twelve 

 singles and five pairs, in quadrant (D) thirteen singles. It will be noticed that one 

 quadrant is more prolific in pairs than the others, and that two quadrants are 

 without pairs. 



In these specimens the umbrella is somewhat flattened out, and measures 17 to 

 22 mm. in diameter. There are about seven centripetal canals in each quadrant. All 

 the specimens show a fair quantity of primary tentacles, but the secondary tentacles 

 have all but disappeared. It was not until a special search was made for them that 

 a few, at a very early stage of development, were found. The fully grown secondary 

 tentacles were probably broken off in the net, and now only their stumps remain. All 

 the four specimens have gonads well developed. 



In my report on the Maldive medusae I stated that the primary tentacles of Olindias 

 did not possess adhesive pads or suckers, and included their absence amongst the generic 

 characters. Mayer and Bigelow have, however, proved the presence of adhesive pads 

 in Olindias tenuis, and no doubt they occur in all the species of the genus. The error 

 on my part arose from using sections of material which had not been specially preserved 

 for that purpose. I failed to distinguish the adhesive cells, and on finding plenty of 

 nematocysts came to the conclusion that the primary tentacles terminated with a battery 

 of nematocysts. 



Distribution. Tropical Pacific and Indian Oceans. 



