Boone, Echinodermata, Cruises of "Ara" and "Alva" 159 



Material examined : Two specimens, taken in coral, Temukus 

 Roads, Bali, Dutch East Indies, October 25, 1931. 



Technical description: Disk pentagonal in the preserved 

 specimens, diameter 18 millimeters. Abactinal surface with the 

 radial shields small, almost or entirely concealed beneath the im- 

 bricated, spine-bearing scales. Some, but not all, of the radial 

 plates are visible near the circumferal border, vanishing beneath 

 the scales. When dissected, the radial plates of a pair are sepa- 

 rated from each other along the inner margins by a wedge-like 

 area covered with imbricated scales, most of which bear long 

 spines. The radial plate has the outer margin sinuate-convex, the 

 lateral margins converging to a subacute apex which extends in- 

 ward less than half the radius of the disk. The abactinal surface, 

 including the radial and interradial areas, is continuously paved 

 by small, imbricated scales, the outer free margin of each is con- 

 vex ; these scales are somewhat irregular shape, about one milli- 

 meter long, or more. They extend abundantly to the circumferal 

 margin and upon the actinal interradial spaces, only the scales 

 near the middle mouth plate and along the margin of the genital 

 slits being devoid of spines. The scales of the disk are practically 

 concealed beneath the numerous long, conical spines, each of 

 which is articulated, the base dilated into a convex knob that fits 

 into its concave support, which is a tabular elevation from a scale, 

 dorsally concave, encupping the base of the spine. The spines are 

 conical, very acuminate, 1.5 to 1.8 millimeters long, with the sur- 

 face covered with fine serrations, arranged in approximate longi- 

 tudinal series, which near and at the apex of the spine become 

 spinules. The central mouth plate is nearly oval, 2.5 millimeters 

 long, 1.5 millimeters median width, with the inner end more nar- 

 rowly rounded and the outer end nearly truncate. The side mouth 

 plates do not meet at the inner apices; each plate is nearly an 

 equilateral triangle, with the outer angle rounded and touching 

 the first under arm plate. The mouth-frame is composed of two 

 elongate pieces, meeting inwardly in the median line and widest 

 here, thence narrowing and extending backward beside and as 

 far as the outer angle of the side mouth plate. There are five 

 mouth papillae, including the proximal one, first tentacle scale, 

 which is a long triangle, basally applied to half of the inner mar- 

 gin of the side mouth plate and also applied on the outer lateral 

 margin to the first small ventral arm plate and apically has a long 



