144 ECHINOIDEA. 
Distribution. Both sides of N. Atlantic from W. Indies to Rockall. 
103-547 fms. 
a-k, 45 miles off Blackrock, 500 fms. Royal Dublin Society. 
l,m. 45 miles off Blackrock, 500 fms. Royal Irish Academy, 
n. A dried fragment, marked “type of Cal-  ‘ Porcupine’ Exp. 
veria hystrix.” 
o. Two dried fragments, marked “Sp. 1, ‘ Poreupine’ Exp. 
fenestrated.” 
2. PHORMOSOMA. 
Phormosoma, Wyv. Thoms. Phil. Trans. clxiv. (1874) p. 732; Duncan, 
J. fae xxiii. (1889) pp. 42 & 310; Bell, Ann. § Mag. iv. (1889) 
p-. 40/. 
An Echinothurid in which the coronal plates imbricate slightly, 
and the ambulacral plates are narrow; the areol of the tubercles 
that bear the primary spines are deeply sunken, and their impress 
may be seen on the internal surface of the test. The calcareous 
deposit in the coronal plates is greater than in Asthenosoma, and 
there are no yertical muscular bands dividing the ccelom into 
separate chambers. The organs of Stewart are not known to be 
ever well developed. 
1. Phormosoma placenta. 
Phormosoma placenta, Wyv. Thoms. Phil. Trans. clxiv. (1874) 
p- 782, pls. lxit. & Ixiii. figs. 1-8; A. Ag. Bull. M. C. Z. x. 
(1883) p. 301, pls. xii. & xv. figs. 3-19; wd. Proc. Roy. Soc. Ed. 
xi. (1883) p. 697; Rathbun, Proc. U. S. Nat. Mus. ix. (1886) 
p. 267; Bell, Ann. § Mag. iv. (1889) p. 436. 
Phormosoma sigsbei, A. Ag. Bull. M. C. Z. viii. (1880) p. 75. 
A species with very large primary tubercles, which are more 
numerously developed on the oral than the aboral surface; they 
have well marked areole, and from what is known as to their spines 
it is probable that they are rather long and have a stout calcareous 
cap: these tubercles are both ambulacral and interambulacral in 
position. There are but few other tubercles on the surface above 
the ambitus, but below, and especially near the mouth, there are a 
number of tubercles, which are also developed on the transversely 
elongated peristomial plates. Organs of Stewart vestigial. 
Colour deep purple below, grey above, with spots and patches of 
purple. 
Diam. of calye. 
Diam. of test. Diam. of mouth. area. 
125 36 20 
110 5b4 18 
100 32 18 
95 24-5 SPS 
80 21 14:5 
Distribution. Both sides of Atlantic, as far south as the Lesser 
