19 



forming along the arms on each side of the ventral furrow 3 rather regular longitudinal 

 rows (see Tab, I, fig. 14). There will most frequently be found on each adambulacral plate 



3 such spines (ibid. 2, 3, 4) situated in an oblique transverse row, and diminishing rapidly 

 in size towards the medial line. Each of these spines belongs thus naturally to a different 

 longitudinal row. The exterior and largest of them (2) issues from about the middle of the 

 ventral side of the adambulacral plate, and is here articulated with a very distinct projecting 

 rounded knob or tubercle; it is usually directed obliquely downwards and a little outwards, 

 and in the exterior part of the arm exceeds the breadth of the arm. The next spine (3) is 

 considerably smaller, scarcely '/a as long, and usually pointing straight downward. And last- 

 ly the interior spine (4) issuing from the interior adoral angle of the adambulacral plate, is 

 very small, and points inwards towards the ventral furrow between the extended water-feet. 

 In very young specimens (see fig. 2) these 2 innermost spines are yet undeveloped; so that 

 there is only a single longitudinal row of furrow-spines along the middle of the adambulacral 

 areas. But in older specimens, the number of the furrow-spines often increases considerably; 

 so that along the interior edge of the adambulacral plates there may be found 2, 3 or even 



4 small spines, all apparently belonging to the interior longitudinal row (see Tab. IV, 

 fig. 16). 



On the lower side of the disc (see Tab. I, fig. 2 & 5) these furrow-spines are con- 

 tinued on each side of the ambulacral furrows up to their extremities at the bucal area. 

 They are also here attached to the 2 pairs of adambulacral plates which form the boundary 

 of the ventral furrow of the disc; so that a somewhat larger spine always issues from the 

 middle of each of these plates; while the others stand nearer to the edge, which is turned 

 towards the ventral furrow (see Tab. IV, fig. 2). The number of these spines is also here 

 somewhat variable according to age. But from the interior border (turned towards the 

 mouth) of the innermost adambulacral plate, there always issue a certain number (usually 3) 

 larger spines pointing horisontally inwards towards the mouth, and which together with the 

 corresponding spines on the adjacent adambulacral plate, form at the end of each of the 

 interradial spaces a regular fan-like outspread fascicle of usually 6 spines, corresponding to 

 the bucal spines in other star-fish. 



All the spines mentioned are in their structure completely similar. The calcareous 

 spine itself is (see Tab. I, fig. 1521) slender, shaped like an awl or like a needle; not 

 echinulated, but smooth and shining and moreover distinctly striped longitudinally. These 

 stripes, which often go somewhat obliquely, or rather spirally, are raised smooth ribs; and 

 in the intervals between them, there may be observed, when strongly magnified, rows of 

 transversely oval holes traversing the hyaline calcareous net of which the spine is composed. 

 Only at the extreme point there appear when strongly magnified (see fig. 17) some short 

 irregularly placed points;' otherwise the spine is quite smooth. At the base the spine is 

 somewhat enlarged, and has a depressed articulating surface, whereby it is articulated with 

 a corresponding elevated knob or tubercle on the ambiilacral skeleton. The articulating 



3* 



