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



present. With this armature the plates have a very echinulate appearance, and the 

 delicacy of the spinelets is remarkable. 



In the median interradial line is a high odd infero-marginal plate immediately below 

 the odd supero-marginal plate. It bears a series of small delicate spinelets along its 

 median vertical line. 



The adambulacral plates are small, with their length equal to, or slightly greater than, 

 their breadth. They are rather widely separate, the' intermediate space being filled in 

 with ligament ; and there is a convex or subangular margin towards the furrow. Their 

 armature consists of: — (1.) a furrow series of three or four small cylindrical spinelets 

 forming an isolated little hand-like comb on the projecting margin ; the fourth or aboral 

 spinelet is often very small, and often absent altogether. (2.) On the actinal surface of 

 the plate are two much longer delicate cylindrical spines, usually placed side by side, but 

 sometimes more or less oblique, the adoral spine being rather more outward in its position 

 than its companion. Occasionally a minute miliary thornlet may be present near the 

 adoral and outer margin of the plate, but there are no other spinelets present. The 

 actinal spines measure about 2 mm. in length near the base of the ray, and the marginal 

 or furrow series are normally less than half this length. 



The mouth-plates are large, and the united pair are broad, convex actinally, and with 

 a prominent free margin towards the actinostome, its outline being more than a semicircle, 

 and slightly flattened anteriorly. The armature consists of a marginal series of eight small 

 cylindrical spinelets on each plate, the two innermost being longer and more robust than 

 the others ; the four innermost on each plate stand parallel to one another and are 

 directed horizontally towards the centre of the actinostome. On the actinal surface of the 

 plate are three or four cylindrical tapering spinelets more robust than the actinal spinelets 

 on the adambulacral plates, arranged rather wide apart, and sometimes rather irregularly, 

 in a line parallel to the median suture ; and one or sometimes two similar and equal 

 spines on the anterior part of the plate iu the interspace between the lineal series just 

 mentioned and the marginal series. No other spinelets are borne on the plates. 



The actinal interradial areas are very small ; and the intermediate plates are few in 

 number and do not extend beyond the fifth adambulacral plate. There are usually two 

 large spiracle-formed pedicellarian apparatus in each area, one on each side of the median line, 

 which occupy nearly the whole space between the mouth-plates and the marginal plates ; 

 sometimes, however, only one is present ; sometimes a second pair occur, rather smaller, 

 and placed on each side of the odd infero-marginal plate, but sometimes in like manner 

 only one of these is present. These double-combed or spiracle-like apparatus are larger 

 and more complex in this species than in any other form I know ; they are also composed 

 of more numerous spinelets and the two opposing series are directed considerably upwards 

 into the cavity of the apparatus, the external margins being prominent and apparently raised. 

 The anal aperture is subcentral and distinct. 



