24 THE VOYAGE OF H.M.S. CHALLENGER. 
A large number of recently discovered species are associated together by community of 
character in the genus Pontaster. 
The following scheme will serve as an index of reference to their “ special marks” :— 
Synopsis of the Species included in the Genus Pontaster herein described. 
A, Adambulacral plates with a secondary series of two or more spines. 
a, Secondary spines on adambulacral plates large and robust; in oblique trans- 
verse series. With more or less well-developed dorsal spines on the 
supero-marginal plates. 
a, One infero-marginal spine and sometimes a small companion, With 
no large spines on the disk. No comb-formed pedicellariz, 
«, With narrow marginal plates confined entirely to the lateral 
wall. 
i, With pedicellariz. Disk large, rays much expanded 
at the base. , j tenuispinus. 
. With no pedicellarie. Disk eal rays an een 
expanded at the base. 
Ie With very fine needle-like spinulation . : planeta. 
. With robust truncate spines : hebitus, 
8. With tread oan plates forming a well-defined boris 
on the abactinal surface. No pedicellarie . : limbatus. 
6. Three infero-marginal spines. With large spines on the disk. With 
comb-formed pedicellarie  . oxyacanthus. 
b. Secondary spines on the adambulacral plates Surtih nl eral to the Saas 
series; in two converging series. With no dorsal spines on the 
supero-marginal plates, or only small ones here and there. : teres. 
B, Adambulacral plates with a secondary series consisting of only one large (eaten 
spine. 
a. With narrow supero-marginal plates. 
a. With quadrivalvate pedicellarie.  Paxille well-developed, with 
several spinelets. 
a, Pedicellariz numerous on the abactinal surface, and on the 
actinal surface extending along the ray on the infero- 
marginal plates. Infero-marginal plates with close 
conical granulation. No secondary lateral spinelet . forcipatus. 
£. Pedicellarie few, only present on the actinal interradial area. 
Infero-marginal plates almost naked. A pais 
secondary lateral spine present . : mimicus. 
6, No pedicellarie. Paxille on the outer part of the ray Benrccented 
only by a squamous plate with a single central spinelet . : pristinus. 
b. With broad supero-marginal plates. No quadrivalvate pedicellarie. 
a. Dorsal spines on the supero-marginal plates long, tapering and 
robust. 
«. Paxille with a central spine, often long and conical. No 
pedicellaria, Actinal intermediate plates present : venustus. 
8. Paxille with no central spine, simple. Comb-formed pedi- 
cellarie. No actinal intermediate plates. : é trullipes. 
b. No dorsal spines, only tubercles, No pedicellariz present . : subtuberculatus. 
