Bd. VI: 4) THE ECHINOIDEA. 83 



pairs of double pores have been developed, and at about 9 mm. length they are 

 already distinctly petaloid, with 4 — 5 pairs of pores in each series. 



In the arrangement of the tubercles no regularity is seen; it should only be 

 noticed that the rather prominent tubercle found on each of the 5 primary inter- 

 ambulacral plates round the peristome remains distinct till a rather late stage; that 

 on the labrum may even be distinct in grown specimens. 



The peristome is originally circular, the mouth 

 opening being in its centre. As seen by the figures 

 on PI. IX the change in the shape of the peristome 

 is produced mainly by the first plate of the odd poste- 

 rior interambulacrum, the labrum, growing forwards, 

 gradually covering the posterior part of the peristome 

 and, at length, also the mouth opening. — Agassiz 

 (Pan. Deep Sea Ech. p. 212) points out that in the ^"'ë- 23- Apical system o( m„ü,s 



cavernosus, iS mm. in length. '°/>. 



young all the mterambulacra are m contact with the 



peristome, »though in older specimens (PL 99. Fig. 8) the posterior lateral ambulacra 

 are excluded from the actinostomes. Apart from the lapsus calami, sambulacra» for 

 interambulacra, it may be pointed out i) that in the figure quoted only the right 

 posterior interambulacrum is shut out from the peristome, and 2) that this is no 

 constant feature of the species; it seems to be more commonly the case that all 

 the interambulacra remain in contact with the peristome, though only very narrowly, 

 as in the left posterior interambulacrum in the figure given by Agassiz (Op. cit. 

 Pi. 99. 8). 



The pores of the madreporite do not increase in number until a rather late 

 stage (comp. Pigs. 19—22); in specimens of about 8 mm. length there may as yet 

 be only a single pore, though, on the other hand, the second pore may appear 

 somewhat earlier. — The first indications of the genital pores have been found in 

 a specimen of 18 mm. length (Fig. 23). 



Abatus Philippii LuvÉN. 



PI. XI, Figs. 6, 9—13. PI. XIX, Fig. 47. 



Abatus Philippii LovÉN'. 1S71. Om Echinoideernas byggnad. Ofvers. Vet. Akad. Forh. N:o 8, p. 6. Fig. i. 



— — LovÉN. 1874. Etudes sur les Échinoidées. PI. XI, fig. 99. PI. XXIX, figs. 188—190. 



— — LovÉN. 1883. On Pourtalesia, p. 73. PI. VIII, Figs. 63, 77. PI. X, Fig. 91. 

 Hcmiaster — A. Agassiz. 1873. The Echini collected on the Hassler-Expedition. Bull. Mus. Comp. 



Zool. in. No. 8, p. 189. 

 — — A. Agassiz. 1874. Zoological Results of the Hassler Expedition. Illustr. Catal. Mus. 



Comp. Zool. VIII, p. 20. PI. IV, Figs. 4— S. 

 Tripylus cavernosus Bernard. 1895 Échinides . . .du Cap Horn. Bull. Mus. d'hist. nat. N;o 7. p. 2. (pro parte). 

 Non: Ilemiaster Philippii Wyv. Thomson. 1877. The .Atlantic II. p. 229 — 34 (= A. cordatus). 



