A8TER0IDEA OF THE MERGUI ARCHIPELAGO. 



323 



margin surrounded by eight to twelve rather longer claviform 

 spinelets, which radiate horizontally. There is a little diminution 

 in the size of the paxillae towards the centre of the disk, and 

 much crowding, but no trace occurs of any epiproctal prominence 

 or peak whatever, its position being frequently occupied by a 

 slight invagination. The paxillae are arranged in short transverse 

 rows at the sides of the rays, the irregular median space being 

 broad. The paxillae become very small towards the end of the 

 ravs. 



mf 



The supero-marginal plates, which are about thirty in number 

 from the median interradial line to the extremity, are small, rather 

 higher than broad, the disproportion of the dimensions being 

 greatest at the base of the ray, and appear slightly tumid when 

 viewed from above. They are covered with papiliiform granules 

 which are uniform in size and shape, and not very closely placed ; 

 and fine cilia are present in the furrows between successive plates. 

 Each supero-marginal plate bears near its abactinal margin a 

 single erect tapering spinelet, the size of the spinelets decreasing 

 gradually along the ray. 



The infero-marginal plates, which are broader than high, extend 

 slightly beyond the level of the superior series, and form a gently 

 rounded curve towards the actinal surface. Each plate bears a 

 single elongate, delicate, subcvlindrical, sharply pointed lateral 

 spine, directed horizontally and at an angle of about 45° to the 

 axis of the ray. Behind the lateral spine is a single small com- 

 panion, similar in shape and character, but not more than one 

 third the length. In large specimens the first miliary spinelet or 

 squamule near this spine may be larger than any of the others; 

 but there is no trace whatever of a transverse series of spinelets 

 along the aboral margin of the plate. In large specimens there 

 may also be a single small spine above and external to the large 

 lateral spine. The surface of the plate is covered with short 

 papiliiform spinelets rather than squamules, which are robust, 

 uniform, and widely spaced ; and the furrows are occupied by 

 numerous, more delicate and cilia-like spinelets. 



The armature of the adambulacral plates consists of short and 

 rather robust spines, which form only two distinct series. The 

 inner or furrow series consists of three short, cylindrical, slightly 

 tapering spinelets, which radiate apart and arch over the furrow r , 

 the middle spine being longest. The outer series consists of two 

 unequal spinelets, the aboral one being very large, robust. 



