CALLIDERMA LATUM. 13 



infero-marginal plates as seen in the margin is a little greater than their length. 

 The height of the supero-marginal plates is, however, somewhat greater. 



The whole superficies of the plates is covered with circular punctations of 

 irregular size rather than hexagons, as in the other forms, and the irregularity 

 caused by the presence of larger punctations here and there is remarkable. This 

 character seems to indicate the former presence of an irregular-sized granulation. 



The supero-marginal plates are similar in character to the infero-marginal 

 series, but the large irregular punctations are larger and more numerous. 



The adarabulacral plates are broader than long, and they bear upon their 

 surface five or six ridges parallel or subparallel to the arabulacral furrow, each with 

 prominent well-defined granulations or elevations, all uniform and closely placed, 

 upon which the adambulacral armature of spines was previously borne (see PL II, 

 fig. Irf; PI. Ill, fig. 2?>). 



The actinal interradial areas are large, and are covered with comparatively 

 large polygonal and rhomboid intermediate plates, which arc arranged in series 

 parallel to the ambulacral furrow, and originally formed a compact tessellated 

 pavement. In a number of the fossils of this species, however, these plates are 

 often separated and displaced, which leads to the inference that in life the plates 

 were not so intimately connected as in other species, and that membrane or con- 

 nective tissue was more largely developed. The one or more series of plates 

 adjacent to the adarabulacral plates are much larger than the others, and none of 

 the intermediate plates extend beyond the base of the ray. The surface of the 

 plates is covered with large, irregular, and rather deeply sunken pits, the 

 character of which leads to the inference that the granulation originally present 

 was also somewhat irregular in size and coarse in character (see PI. II, fig. 1 c ; 

 PI. Ill, fig. 1 e). 



In some examples (notably in that figured on PL III, fig. 2 a) small oval fora- 

 minate pedicellarise, distinctly lipped at the margin of the foramen, are present on 

 the actinal intermediate plates. 



The mouth-plates are elongate, about three times as long as broad, triangular 

 in shape, with the two outer sides subequal. Their surface is covered with large, 

 coarse, irregular, tuberculose elevations (see PL II, fig. 1 e), which suggest the 

 inference that the armature of the mouth-plates consisted of large, irregular, 

 papilliform granules. 



In some examples a portion of the actinal floor has been removed, exposing the 

 inner surface of the abactinal floor. In these cases the stellate base of the abac- 

 tinal plates or paxillae are seen (see PL II, figs. 2 a, 2d; PL III, figs. 3 a, 3 b). It 

 will be noticed that there is a difference in the form of the stellate bases in these 

 examples, which may indicate a specific or varietal difference, but I do not feel 

 justified from this character alone in recognising either of these fragments as the 



