88 " ENDEAVOUR " SCIENTIFIC RESULTS. 



Ophiactis symbiota,! sp. nov. 

 (Plate XXX vi., fig. 1-2.) 



Disk 6.5 mm. in diameter ; arms about 26 mm. long. 

 Disk covered by a coat of 150-200 rather coarse, flat, rounded 

 scales, the largest of which are near centre and the smallest near 

 interradial margins ; between these plates or on their corners 

 or edges are low, conical tubercles which increase in length 

 near the interradial margins, becoming short sharp spinelets ; 

 these tubercles and spinelets are not very numerous, some 

 plates having none, while the largest plates have only 5-6 

 around them. Radial shields small, about 1 mm. long by 

 .5 mm. wide, well separated within but sometimes in contact 

 distally. Upper arm plates, fan-shaped, truncate proximally, 

 strongly convex distally, with lateral corners more or less 

 rounded or truncate. Interbrachial areas below covered 

 like the interradial margins of disk, with rather small scales 

 and numerous sharp spinelets. Oral shields pentagonal, 

 widest proximally, disto-lateral sides concave, distal side 

 shortest ; madreporite very much larger than other four and 

 more iso -pentagonal. Adoral plates large, twice as long as 

 broad, curved, meeting broadly within. Teeth about 6, 

 squarish ; below the lowest is a very small, triangular dental 

 papilla. Oral papillae apparently 2 on a side but the proximal 

 may be the scale of the inner oral tentacle-pore ; distal 

 papillae nearly circular, about .20 mm. in diameter ; proximal, 

 a trifle smaller and more angular. First under arm -plate 

 relatively large, longer than wide, in contact with second, thus 

 broadly separating the adoral plates ; succeeding plates 

 tetragonal, wider than long, with distal margin shghtly con- 

 vex and lateral margins concave, becoming, beyond the middle 

 of arm, pentagonal with a proximal angle and longer than 

 wide ; first 5 or 6 barely in contact. Side arm plates rather 

 large meeting above and below at middle of arm and beyond ; 

 each carries 4, or usually 3, opaque, stout, blunt spines ; upper- 

 most longest, about 1 mm. long ; lowest, shortest, about .60 

 mm. long. Tentacle-scale single, moderately large, at side 

 of lower arm-plate. Colour (dry), brownish- white. 



This interesting Ophiuran, I found on a specimen of Com- 

 anthus plectrophorum, clinging closely to the oral surface of the 

 disk. Its position leaves Uttle doubt in my mind that it was 

 commensal with the Crinoid in life, as a number of species of 

 Brittle-stars are known to be. It is utterly unlike 0. 



1- (TW/i/3<oTos= living with ; in reference to the apparently symbiotic 

 iiabits. 



