90 



PROF. P. M. DUNCAN ON THE OPHIUKID^! 



filiform at the end, flat below, and convex above. Lower arm- 

 plates very broad, broader than long, twice as broad as long for 

 some distance beyond the disk, nearly quadrangular near the 

 disk, and with a point at the median line adorally, incurved 

 aborally lower down, with an inward curve at the sides for the 

 tentacular opening. A low, broad elevation runs along the 

 median line of each lower arm-plate. 



Upper arm-plates large, much broader than long near the disk, 

 slightly convex adorally from side to side ; the aboral edge 

 is the widest, and the adoral is boldly curved adorally. Further 

 out the plates are elliptical and broader than long, bnt near the 

 tip the length increases over the breadth. The side arm-plates 

 are small flaps close to the arm, which soon encroach slightly 

 between the upper and lower plates, and the separation of the 

 upper arm-plates by them soon becomes considerable. 



Three short, cylindrical, pointed spines stick out widely from the 

 arm and from each other, the middle one the longest and thickest. 



Two tentacle-scales over the large tentacular openings, broad 

 and pointed — one is on the side arm-plate, and the other on the 

 lower arm-plate. They reach far out in the arm, and the scale 

 attached to the lower arm-plate becomes longer. Diameter of 

 disk 45 millim. Length of arm 26 millim. Colour white and 

 flesh-tinted. 



Localities. Elphinstone Island and King Island. 



One of the commonest species of the Ophiurida in the Archi- 

 pelago is a small, slender, long-armed form, which is usually found 

 without atop to the disk, and, moreover, the middle of the upper 

 arm-plates is wanting for some little distance beyond the disk. 

 The genital plates and scales, the interbrachial parts, and the 

 whole of the top of the disk are then absent. In two instances 

 the disk has been preserved, and it is possible therefore to describe 

 the species fully and to classify it. 



Ophtoimiuaomus difficilis, sp. nov. (Plate VIII. figs. 7-9.) 



The disk is small, flat, strongly pentangular, with a well-defined 

 re-entering curve at the margin between the radial shields. 



Diameter 5 millim. Length of arm 70 millim. Disk covered 

 with B minute overlapping scaling except on the radial shields. A 

 large scaling at the margin* Radial shields long and narrow, but 

 forming much of the disk, and close except midway; the ends 



