SEA LILIES, STARFISHES, ETC. CLARK. 41 



in alcohol, brownish-yellow ; dry, pale brown. Seven 

 specimens. 



This fine species is obviously near to Mediaster ornatus, 

 Fisher, from the Hawaiian Islands, but differs in the wider, 

 shorter marginal plates and in the adambulacral armature. 

 No other member of the genus is very closely alhed. As 

 regards the internal anatomy, the Austrahan species is a 

 typical Mediaster, the internal abactinal ossicles being very 

 evident and rudimentary superambulacral plates also being 

 present. 



Logs. — East coast of Fhnders Island, Bass Strait, 40 

 fathoms. This specimen has been selected as the holotype. 



East of Babel Island, Bass Strait, 65-70 fathoms. 



Oyster Bay, Tasmania. 



Mediaster monacanthus,i sp. nov. 



(Plate X., fig. 1-2 ; Fig. 4.) 



R = 110 mm. ; r=37 mm. ; R=3 r. Br=37 mm. ; R = 

 3 br. Br at middle of ray =19 mm. ; at tip =5 mm. Disk 

 large, flattened or shghtly elevated ; arms wide at base, 

 tapering rather evenly to the blunt tip. Abactinal plates on 

 disc and base of rays large, low, hemispherical, widely spaced, 

 becoming smaller and more and more crowded near the supero- 

 marginals ; they are connected with each other by heavy 

 radiating ossicles, in the spaces between which the papulae 

 arise in groups of 3-15. Each plate is covered by a coat of 

 low, spherical granules ; there are about 50-75 on a plate 4-5 

 mm. in diameter ; there are no granules on the membrane or 

 on the ossicles between the plates. In the holotype, and some 

 other specimens, most of the disk plates bear at the centre a 

 pointed tubercle or low, blunt spine, about a millimeter in 

 diameter and nearly or quite as high ; in some specimens few 

 or no plates have this spine, so it may be an indication of 

 complete maturity. Distally on the rays and near the 

 margins of the disk, the plates become smaller and crowded, 

 so the granular covering is nearly or quite continuous. 

 Madreporite very small, only about 2 mm. across, situated 

 twice as far from the margin as from centre of disk. Anus 

 conspicuous near centre of disk because surrounded by 10-20 

 large, smooth, elongated granules of diverse size and shape. 



1. y«oVos=single+ tt'/ca»'0«= a thorn or spine ; in reference to the single 

 prominent spine on some abactinal plates. 



