24 ON THE ECHINODEEMATA OF THE 



the ray stands at the same angle to the plate, and thus two regular rows are formed on 

 either side of the furrow. In others, however, each alternate pair of spinelets radiate 

 at a rather smaller angle to the floor of the ray, the internal spine being directed 

 further over the furrow, and the external one standing opposed to the interspace between 

 the pairs of spinelets of the neighbouring plates ; by this means an arrangement of 

 four rows of spinelets on each side of the furrow is brought about, which, together 

 with the swollen character of the sides, gives an appearance of considerable breadth to 

 the ventral portion of the rays. The ambulacral spines are long, cylindrical, and 

 rounded at the tip, not tapering or pointed in the slightest ; and the innermost spine is 

 somewhat thinner than the others. Pedicellarise forficiformes are very numerous 

 amongst the rows of ambulacral spinelets, and are densely crowded at the base of the 

 rays in large specimens. The lateral spines, which are long, cylindrical, and somewhat 

 crumpled or nipped together at the tip, form three longitudinal rows extending along 

 the ray. In addition to these there is a short secondary row situate between the most 

 ventral of the lateral series and the ambulacral spines ; but, in consequence of the 

 rapidity with which the spinelets diminish in size as they proceed outwards, this series 

 extends only along the inner half of the ray. 



In some large specimens there is often a short row of 6-8 supplementary spines at 

 the base of the ray between the ventral and middle series of lateral spines ; or a 

 tendency to reduplication may be shown even in each of the rows at the extreme base 

 of the ray. Occasionally the lateral spines are more or less tapering, those of the 

 dorsal and median rows being also slightly curved upward. 



The calcareous network of the abactinal surface is very robust, the membranous 

 meshes or interspaces being in proportion comparatively small. The papula3 are, as a 

 rule, single in young specimens; but in those of larger growth two or three occur 

 together. The dorsal spinelets are large and cylindrical, not tapering, but nipped 

 together at the tip, or even sometimes subclavate as in A. violaceum. They do not 

 assume any lineal or regular arrangement whatever upon the abactinal surface. In 

 some examples the dorsal spinelets are closely surrounded by a number of rather 

 smaller subclavate spinelets, which give the appearance of compact groups of spines 

 crowded together upon the abactinal surface of disk and rays alike. 



Pedicellarise forcipiformes, although very numerous upon the abactinal membrane, 

 cannot be strictly said to form regular wreaths at the base of the dorsal spines ; for 

 whilst in some places they are much crowded, in others only three or four are present. 

 In the lateral series, however, the spines of the upper or dorsal row are surrounded at 

 their bases by a true wreath of pedicellaria?, whilst in the ventral or lower row the 

 pedicellariae are principally grouped on the dorsal or upper side of the base. 



The pedicellarise forficiformes, which are moderately numerous upon the abactinal 

 surface, averaging perhaps one or two to a mesh, are densely crowded amongst the rows 

 of ambulacral spines, especially on the innermost portion of the furrow. These pedi- 

 cellariaB (p. forficiformes) are in the present species comparatively small, only a little 

 longer than broad, and dumpy in form ; the p. forcipiformes, on the other hand, are 

 large, very gibbous, and truncate at the apex of the jaws. 



