64 PAJSTAMIC DEEP SEA ECHINI. 



miliary spines. The primary radioles are of a still lighter tint, somewhat 

 pinkish. 



In a specimen 20 mm. in diameter the apical system measured 14 mm. 

 in diameter (PI. 28, figs. 1, :?) and the anal system 10 mm. The genital 

 and ocular plates are more elongate than those of D. gbbubsum, in which 

 the genital plates specially project further into the anal system than in 

 D. horridum ; compare Plate 28, figs. J, 2 with Plate 28, figs. 3, J,. The 

 greatest width of the ambulacral system, 2.3 mm., is found nearer the ambi- 

 tus than to the equatorial zone. The actinal system (PI. 26, fig. /) is mm. 

 in diameter ; the height of the test is 12 mm. At that stage of growth 

 there are nine primary interambulacral tubercles, Fig. 94, with a tenth 

 rudimentary plate (PI. 26, fig. J f ). 



There are four ambulacral plates to each of the larger interambulacral 

 plates (PI. 29. fig. /,). The muscular furrows of the scrobicular area are 

 well developed. An irregular row of two or three miliaries occupies the 

 upper part of each ambulacral plate, Fig. 95 (PI. 29, fig. 3); these become 

 small secondary tubercles on the older plates (PI. 26, fig. 4). The miliaries 

 along the sides of the median interambulacral line are irregularly arranged, 

 filling the spaces between the scrobicular circles; these unite at the sutures. 

 A similar belt of miliaries fills the angles between the scrobicular areas and 

 the ambulacra. The miliaries of the interambulacra are more uniform in 

 size than those of the ambulacra. 



The genital plates are elongate, Fig. 96, pentagonal, with slightly 

 rounded corners; they are covered with miliaries and pierced by large 

 genital openings placed in the centre of the plate ^Pl. 28, figs. 1, 2). The 

 ocular plates are even more elongate than the genitals ; the rounded 

 corners of adjoining plates leaving a slight notch between the genitals 

 and oculars. The ocular pore is on the edge of the plate close to the 

 terminal ambulacral plates. 



The ten buccal ambulacral plates (PI. 26, fig. 1) are smooth, irregularly 

 triangular, they join along their whole length ; the outer face is slightly 

 concave. The proximal extremity is cut oft* to form the dental pentagon ; 

 at the junction of the teeth with the actinal membrane it is strengthened 

 by a number of filaments carrying minute calcareous plates. The ten- 

 tacular pores are placed in the distal third of the plate; in younger 

 specimens they are nearer the distal sides (PI. 25). The actinal membrane 

 between the buccal plates and the coronal plates (PI. 26, fig. 1) is thickly 



