THE ECHINOIDEA. 
Bd. VI: 4) 
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 
young all the interambulacra are in contact with the 
peristome, »though in older specimens (PI. 99. Fig. 8) the posterior lateral ambulacra 
are excluded from the actinostome». Apart from the lapsus calami, »ambulacra» for 
interambulacra, it may be pointed out 1) 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. 
PL 99. 8). 
The pores of the madreporite do not increase in number until a rather late 
stage (comp. Figs. 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). 
Fig. 23. Apical system of Abattis 
cavernosus , 18 mm. in length. s %. 
Abatus Philippii LovÉN. 
PI. XI, Figs. 6, 9-13. PI. XIX, Fig. 47. 
Abatus Philippii Lovén. 1871. Om Echinoideernas byggnad. Öfvers. Vet. Akad. Förh. N:o 8, p. 6. Fig. 1. 
— Lovén. 1874. Etudes sur les Échinoidées. PI. XI, fig. 99. PL XXIX, figs. 188 — 190. 
— — Lovén. 1883. On Pourtalesia, p. 73. PI. VIII, Figs. 63, 77. PI. X, Fig. 91. 
Hemiastet — • A. Agassiz. 1873. The Echini collected 'on the Hassler-Expedition. Bull. Mus. Comp. 
Zool. III. 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—8. 
Tripylus cavernosus Bernard. 1895 Échinides . . .du Cap Horn. Bull. Mus. d’hist. nat. N:o 7. p. 2. (pro parte). 
Non: Hemiaster Philippii Wyv. Thomson. 1877. The Atlantic II, p. 229—34 (= A. cordatus). 
