74 



ECHINOIDEA. II. 



pushed far backwards, separated from the small inner plate at the peristome not onh- by the anibu- 

 lacral plates IV. b. 2 — 4 and II. a. 2 — 3, the po.sterior one of them being much prolonged backwards 



along the ambulacral plates V.a.i and 

 I. b. I, but also by the interambnlacral 

 plates4. a. 4 and i.b. 4 — 5, which join 

 the ambulacral plates \'. a. i — 2 and 

 I. b. I — 2 for a long way. The plates 

 I. a. 4 and 4. b. 4 are very much en- 

 larged, and upon the whole all the 

 plates of these interambulacra are 

 unusually large. As in pliinlc these 

 interambulacra are \ery nnich bent 

 upon themselves, the median part 

 being near the posterior end, where- 

 as the upper and lower end is at 

 the anterior end of the animal. That 

 the interpretation of the plates given 

 here is correct seems beyond doubt, 

 from a comparison with P. phialc 

 (Fig. 10), in which the interpretation 

 lies quite evident. — The plates of 

 the antero-lateral ambulacra and in- 

 terambulacra are rather small, in 

 accordance with the small size of 

 the <head». The odd anterior am- 

 bulacrum contains ca. 14 pairs of 

 plates ; I have been unable to count 

 the number with full certaint}-. The 

 invagination is comparatively small, 

 but otherwise of the usual form. 

 The peristome is almost round, cov- 

 ered with rather large plates. The 

 nuiuth is a little below the middle. 

 The apical system is sitiui- 

 ted near the anterior end; from the 

 outside I was unable to see the 

 limits of the plates in this region 

 with any certaint\-, but from the inside most of them could be distinctly seen (Fig. 14). Probably the 

 plate just behind the large inner prolongation from the madreporic plate will really be divided in 

 two, but I could not distiugui.sli any line there. Also the small iunennosl ])lale of llie antero-lateral 



Fig. 13. .\nalysis of part of the test of Pourlalcsia paradoxa. 



