90 THE VOYAGE OF H.M.S. CHALLENGER. 



than the rest, which are subequal in length. When standing upright they are parallel to 

 one another, and when directed over the very narrow ambnlacral furrow, radiate only to a 

 slight degree, often not at all. The succeeding combs thus formed are distinctly spaced. 

 (2.) On the actinal surface of the plate is borne a lineal series of three or four subclavate 

 or subfusiform, papilliform, spinelets, parallel to and close behind the furrow series. These 

 are more robust, but slightly shorter, than the marginal series, and are well spaced apart. 

 External to these, and with a well-defined space between, are two irregular series of short, 

 robust, obtuse, papilliform granules, which have a tendency to associate themselves into 

 groups of three or four, suggestive (but probably nothing more) of incipient pedicellarise. 

 Occasionally on the larger plates one or two supplementary thornlets or papilliform granules 

 may be present between these groups and the papilliform series of spinelets next to the 

 marginal series. On the outer fourth of the ray the adambulacral plates bear a single 

 conical-pointed spinelet, external to the furrow series, which increases in size as the 

 extremity is approached. No trace of this spine is found on the plates along the inner 

 part of the ray. 



The mouth-plates are small and narrow ; the united pair have an elongate elliptical 

 outline, and are slightly convex actinally. Nearly half their length is free and protrudes 

 over the actinostome, which they can completely close in. Their armature consists of a 

 marginal series of nine or ten, or more, short papilliform mouth-spines on each plate, which 

 decrease in length as they recede from the mouth, and stand upright and parallel to one 

 another on the free margin. The actinal surface of the plate is covered with numerous 

 papilliform granules which increase in length and robustness as they approach the 

 inner extremity, where they are very robust and definitely papilliform, even longer than 

 the marginal series of true mouth-spines. 



The actinal interradial areas are large and well-developed, and intermediate plates extend 

 up to nearly half the length of the ray, the outer ones, however, being very narrow and 

 long. The areas are occupied by well-defined plates arranged in regular series or columns, 

 extending from the adambulacral to the marginal plates. The innermost plate of each 

 series is normally subequal in breadth to the adjacent adambulacral plate, and the columns 

 diminish in breadth as they proceed towards the margin ; but the columns generally in- 

 crease in breadth as they proceed along the ray, whilst their length diminishes pari passu, 

 hence the narrow band-like plates on the outer part of the actinal area noticed above. 

 The surface of the plates is covered with numerous small papilliform granules, nearly 

 similar to those on the actinal surface of the adambulacral plates, disposed in regular 

 subrectangular groups, each group marked out from its neighbours by distinct channels, 

 and indicating conspicuously the regularity of the arrangement of the plates. There is 

 usually on each plate a group of three or four papilliform granules slightly larger than the 

 others, simulating an incipient pedicellaria, similar to those mentioned on the adambulacral 

 plates ; and in some cases two such groups are present. 



