REPORT ON THE ASTEROIDEA. 125 
of the plate. Sometimes one of these spinelets might almost be counted as belonging 
to the oblique series just mentioned, and sometimes one of them is wanting. 
The occurrence of the pedicellarize on the adambulacral plates in this species is very 
erratic, some examples being well provided, while others have very few. The pedi- 
cellarize, which are large and highly developed, have been figured and described by 
Perrier.’ A similar irregularity in the occurrence of the pedicellarise has been noticed 
by De Loriol* in Archaster angulatus; and I have observed the same fact in specimens 
from Mauritius in my own collection. 
Family PoRCELLANASTERID&, Sladen (1883), emend. 1886. 
Rays usually narrow in relation to the size of the disk, more or less produced. 
Marginal plates in superior and inferior series, thin, lamelliform, apparently naked, or 
covered only by an extremely thin epidermal tissue. 
Abactinal area covered with membrane, beset with simple spiniferous spicules or 
pseudo-paxillz, which occupy the whole or only a limited portion of the area. A central 
epiproctal prominence, more or less defined, frequently developed into an elongate tubular 
prolongation. 
Actinal interradial areas more or less extensive, paved with thin squamiform inter- 
mediate or ventral plates, more or less regularly disposed and covered with delicate 
membrane. 
Adambulacral plates elongate, simple, bearing spines (one to five in number) on the 
furrow margin only ; or there may be one or more series of small papilliform granules on 
the actinal surface of the plate. 
Cribriform organs along the vertical sutures of the marginal plates in the interbrachial 
ares, 
Ambulacral tube-feet in simple pairs, with conical pointed tips. 
Madreporiform body usually placed close to the marginal plates. 
Remarks.—In this family are included the genera Porcellanaster, Styracaster, Hypha- 
laster, and Thoracaster, which embrace a series of highly remarkable forms, nearly all of 
them exclusively from great depths, which were first brought to light during the cruise 
of the Challenger. I now associate with them the genus Ctenodiscus, whose structure 
indicates in many ways a community of descent, and shows a much nearer relationship to 
the present group than to the Astropectinidee, with which it has been previously classed. 
In many respects, however, Ctenodiscus differs considerably from the other members of 
the Porcellanasteride ; and its position in the family must, for the present, be regarded as 
1 Recherches sur les pédicellaires, &c., p. 95 (separate copy), pl. 2, figs. 12, 13 (Ann. Sct. Nat., 1869, 
t. xii, p. 287). 
2 Mém. Soc. phys. et hist. nat. Geneve, 1885, t. xxix., p. 79. 
