88 ‘‘ ENDEAVOUR ”’ SCIENTIFIC RESULTS. 
OPHIACTIS SYMBIOTA,! sp. nov. 
(Plate xxxvi., 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 papille apparently 2 on a side but the proximal 
may be the scale of the inner oral tentacle-pore; distal 
papille 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 slightly 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 little 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. oupBiotos=living with; in reference to the apparently symbiotic 
habits. 
