74 



ECHINOIDEA. II. 



pnshed far backwards, separated from the small inner plate at tlie peristome not onh- bv the ambn- 

 lacral piates I\. h. 2—4 and II. a. 2—3, the posterior one of theni being much prolonged backwards 



along the ainbiilacral piates V.a.i and 

 I. b. I, bnt also bj'the interarabulacral 

 plates4. a. 4 and i.b. 4 — 5, whichjoin 

 the ambulacral piates V. a. 1 — 2 and 

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

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

 larged, and upon the whole all the 

 piates of these interambnlacra are 

 nnnsnally large. As in pliinlc these 

 interambnlacra are ver\- mnch bent 

 npon themselves, the median part 

 being near the posterior end, where- 

 as the tipper and lower end is at 

 the anterior end of the animal. That 

 the interpretation of the piates given 

 here is correct seems beyond donbt, 

 from a comparison with P. phiale 

 (Fig. 10), in which the interpretation 

 lies qnite evident. — The piates of 

 the antero-lateral ambulacra and in- 

 terambnlacra are rather small , in 

 accordance with the small size of 

 the <head\ The odd anterior am- 

 bnlacrnm contains ca. 14 pairs of 

 piates; I have been unable to connt 

 the nnmber with fnll certainty. The 

 invagination is comparatively small, 

 bnt otherwise of the usnal form. 

 The peristome is almost ronnd, cov- 

 ered with rather large piates. The 

 montli is a little below the middle. 

 The apical system is sitna- 

 ted near the anterior end ; from the 

 ontside I was nnable to see the 

 limits of the piates in this region 

 with any certainty, bnt from the in.side most of them conld be distinctly seen (Fig. 14). Probably the 

 ]3late jnst behind the large inner prolongation from the madreporic plate will really be divided in 

 two, bnt 1 conld not distinguish an>- line there. Also the small innerinost plate of the antero-lateral 



(Sternum ) 



Sternuivl 



Fig. 13. Analysis of part of the test of Pourtalcsia pai-adoxa. 



