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 Sp>ccies 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 pedicellariae. 

 a. With narrow marginal plates confined entirely to the lateral 

 wall, 

 i. With pedicellariae. Disk large, rays much expanded 



at the base ....... tenuispinus. 



ii. W T ith no pedicellariae. Disk small, rays not much 

 expanded at the base. 



1. With very fine needle-like spinulation . . planeta. 



2. With robust truncate spines . . . hebitus. 

 /3. With broad marginal plates forming a well-defined border 



on the abactinal surface. No pedicellariae . . . limbatus. 



b. Three infero-marginal spines. With large spines on the disk. With 



comb-formed pedicellariae ....... oxyacanthus. 



b. Secondary spines on the adambulacral plates small, and equal to the furrow 



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 conical 



spine. 



a. With narrow supero-marginal plates. 



a. With quadrivalvate pedicellariae. Paxillae well-developed, with 



several spinelets. 



a. Pedieellariae 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 . foreipatus. 



13. Pedicellariae few, only present on the actinal interradial area. 

 Infero-marginal plates almost naked. A well-developed 

 secondary lateral spine present ..... mimicus. 



b. No pedicellariae. Paxillae on the outer part of the ray represented 



only by a squamous plate with a single central spinelet . . pristinus. 



b. With broad supero-marginal plates. No quadrivalvate pedicellariae. 



a. Dorsal spines on the supero-marginal plates long, tapering and 

 robust. 



a. Paxillae with a central spine, often long and conical. No 



pedicellariae. Actinal intermediate plates present . venustus. 



/3. Paxillae with no central spine, simple. Comb-formed pedi- 

 cellariae. No actinal intermediate plates . . . trullipes. 

 b. No dorsal spines, only tubercles. No pedicellariae present . . subtuberculatus. 



