ECHINOIDEA. II. 



the corresponding plates 2, the bivial ambulacra thus not being; interrupted by the interambulacra i 

 and 4. The inner plate of these interambulacra is small, but distinct, at the edge of the invagination 

 it is separated from the corresponding second plate by the ambulacral plates II. a. 2 and IV. b. 2, some- 

 times also IV. b. 3, which are prolonged back-wards so as to join the ambulacral plates I.b. i and V. a. i. The 

 interambulacra i and 4 are much prolonged backwards, and the plates i. a. 4 and 4. b. 4 have especially 

 become very large; in the abactinal part these interambulacra have a forward direction, thus being in 

 some way bent upon themselves (Fig. 10) a feature which is carried to the extreme in P. paradoxa 

 (see Fig. 13. p. 74). In the interambulacrum i in the specimen from which the Fig. 10 was made the 

 plate i. a. 3 is abnormally divided into two; also the plate designated i. b. 4 is evidently abnormal. 



s.t 



3 b.Z 



Fig. 10. Analysis of Part of the test of Ponrtalesia phialc. 

 The plate marked x is probably part of i. a. 3, abnormally separated off from the latter. 



Whether any of these plates should be interpreted as being compound (in the sense of Loven's He- 

 teronomy) I do not venture to decide. 



The periproct is not sunken; it is surrounded by three epiproctal plates on each side, viz. 

 5. a. 6 8 and b. 7 9. The apical system (PL VII. Fig. 7) is disconnected as in P. Jcffreysi; the genital 

 openings are not developed in the specimens in hand. The primary tubercles are not serially arranged. 

 The description and figures of spines and pedicellarise will be given in the Report on the Echi- 

 noidea of the German South Polar Expedition, founded on the single, very beautifully preserved 

 specimen taken by that Expedition. The specimens from the Ingolf are smaller (8 13""") and less 

 well preserved, sufficiently well, however, to show that they agree in every respect so closely with 

 that from the Antarctic Sea that it is quite out of the question to separate them as a distinct species. 

 The question whether the antarctic species described in the < Challenger -Report as P. phialc is really 



