126 THE VOYAGE OF H.M.S. CHALLENGER. 
an isolated one. The structural characters of this genus appear to me to warrant its 
separation in a distinct subfamily. 
The Porcellanasteridz may be said to hold a divergent position between the Archas- 
teridee and Astropectinide, rather than a directly intermediate relation. In some respects 
they appear to present a more archaic character than the Archasteridz, but this, it seems 
to me, is dependent on striking features of structural detail rather than on general facies, 
and, as a matter of fact, is not borne out by the present state of our knowledge of the 
older forms of starfish life. Furthermore, this apparently archaic facies is largely due to 
the remarkable degree in which the Porcellanasteride present permanently characters 
which are regarded, in the majority of forms at least, as essentially embryonic. 
The following table will show the distinctive relations of the genera discussed in the 
succeeding pages, and will serve as a brief epitome of the more prominent superficial 
characters by which they may be recognised. The genera are divided into two subfamilies. 
Synopsis of the Genera included in the Family PorcELLANASTERID. 
A. Cribriform organs highly developed; localised. Actinal interradial areas 
with no fimbriated transverse channels . : ° : : . PoRCELLANASTERINE. 
a. Actinal intermediate plates naked. Adambulacral plates with a single 
series of spines on the furrow margin only. Terminal plates 
large, armed with conspicuous spines. Cribriform organs one 
to nine in number. 
a. With a tubular epiproctal elongation or anal funnel. Abactinal 
membrane with simple spiniferous spicules. Actinal inter- 
mediate plates not imbricated. Ambulacral furrows wide 
and exposed. Rays more or less turned back. Cribriform 
organs one to three, component structure lamelliform . j : . Porcellanaster. 
6. No tubular epiproctal prolongation, but a more or less definite 
conical peak may be present. Abactinal membrane with 
pseudo-paxille. Actinal intermediate plates imbricated and 
arranged in columns. Ambulacral furrows narrow and con- 
cealed. Rays not revertible. Cribriform organs five to nine 
(three in one case only), component structure papilliform. 
a. Rays very long. Supero-marginal plates with long 
robust spines, forming a single series along the 
median line. Spines of adambulacral armature 
long and needle-shaped, radiating apart. Mar- 
ginal plates united along the median line of the 
rays ; . : ‘ 5 : : . : » Styracaster. 
8, Rays short. No spines on the supero-marginal plates. 
Spines of adambulacral armature short, com- 
pressed, forming independent series or fans. : . Hyphalaster. 
bh. Actinal intermediate plates covered with spiniform granules. Adam- 
bulacral plates with papilliform spinelets on the outer portion 
of the plate. Terminal plates very small ‘and inconspicuous ; 
unarmed, Cribriform organs fourteen in number . 5 : : . Thoracaster. 
