CALLIDERMA. SMITHI^. 7 



from the median interradial line to the extremity. They form a broad conspicuous 

 border to the actinal area, the breadth of which diminishes gradually from the 

 median interradial line to the extremity. The largest infero-marginal plates near 

 the median interradial line measure 9 mm. in breadth, and 4 mm. in length ; the 

 length increases a little between this point and the base of the ray, where it is 

 again 4 mm. The breadth decreases step by step from the median interradial line, 

 and at the base of the ray is less than 4 mm., and further out the breadth of the 

 plates is less than the length. The height of the infero-marginal plates as seen in 

 the margin is greater than the length of the plate, the proportions near the 

 median interradial line being as 3 : 2 approximately. The proportion of the 

 height decreases at the extremity of the ray. The infero-marginal plates are 

 slightly convex on their actinal surface and distinctly tumid on their marginal 

 surface. The whole superficies is covered with small, hexagonal, closely-placed 

 punctations, upon which granules were previously borne, probably uniform in size 

 and compactly placed. On a number of the plates are one or more subcircular or 

 irregular shallow concavities, quite irregular in size, position, and occurrence, 

 which I believe to have been caused by the presence of a pedicellarian apparatus, 

 perhaps the cavities of ordinary foraminate pedicellarise enlarged by weathering. 

 These are seen in PI. I, figs. 1 a, 1 b, 1 c, 1 d. I scarcely think that they are the 

 marks left by tubercles or enlarged granules. In the example, however, figured 

 on PI. VIII, fig. 2 (/, small spinelets were undoubtedly present. 



The adambulacral plates are broader than long, their dimensions at a short 

 distance from the mouth being 3*25 mm. broad and 1"75 mm. long. They bear 

 upon their surface four or five ridges, parallel or sub-parallel to the ambu- 

 lacral furrow, each with five or six articulatory elevations upon which spines had 

 previously been borne. A number of these spines are still preserved, irregularly 

 strewed over the surface of the plates. They are short, tolerably robust, slightly 

 flattened, slightly tapering and abruptly rounded at the tip. The longest 

 measures about 1"5 mm. in length, or a little more; their surface is finely striate, 

 in fact so fine that the character is perhaps mainly due to the effect of weathering 

 upon the structural texture of the spine. 



The actinal interradial areas are large and are covered with a great number of 

 small, regular, quadrangular or rhomboid intermediate plates, which are arranged 

 in series parallel to the ambulacral furrow, and form a compact tessellated pave- 

 ment. The average size of the plates is about 2 mm. in diameter, but the plates 

 of the series adjacent to the adambulacral plates are somewhat broader, and the 

 plates near to the infero-marginal plates become smaller and irregular. The plates 

 extend at the base of the ray to about the eighth infero-marginal plate, counting 

 from the median interradial line. The surface of the plates is covered with large, 

 rather widely spaced, hexagonal punctations — the marking left by the granules 



