2 THE VOYAGE OF H.M.S. CHALLENGER 



should have chosen as the type of the family. From the fact, however, that the name 

 has already passed into general use, and that a number of the deep-sea forms have been 

 understood, at least conventionally, as belonging to that family, the designation has had 

 a significance given to it beyond the scope of special students of the Asteroidea. Under 

 these circumstances it seems to me better to avoid confusion by retaining the name of Archas- 

 teridse, than to give a new famdy name based on a genus that would be more generally 

 typical of the group as a whole ; though the latter course would have been undoubtedly 

 preferable if the considerations I have mentioned above had not stood in the way. 



The following tabular arrangement will show the relations of the genera herein 

 described, which are now classed in the family Archasteridae ; and also the four sub- 

 families into which they are naturally divisible. 



Synopsis of Genera included in the Family Aechasteeid^e. 



A. No definite medio-radial line of abactinal plates. 



a. Papulae confined to a limited area at the base of the ray. Marginal 



plates more or less alternate. Actinal intermediate plates 

 absent or very few in number ...... 



a. With large odd interradial marginal plate and spine. No true 



paxillae. Spicule bearing plates only. No special papular organ 



b. No odd interradial plate. True paxillae. Special papular organ 



b. Papulae distributed over the whole abactinal area. Marginal plates 



opposite. Actinal intermediate plates well developed 



a. Marginal plates more or less equally developed in each series. 



a. Supero-marginal plates thin and plate-formed ; con- 

 fined to the lateral wall ; armed with a spine. No 

 order of abactinal plates. Pedicellariae present . 



j3. Supero-marginal plates thick and massive, extending 

 more or less on abactinal surface ; usually un- 

 armed. Abactinal plates along the margin of 

 the ray in more or less definite transverse series. 

 No pedicellariae ...... 



b. Supero-marginal plates almost aborted .... 



B. "With a definite medio-radial line of abactinal plates. 



a. Abactinal plates arranged in longitudinal series parallel to the 



median series. No internal imbricating ridges. Actinal inter- 

 mediate plates well developed. No pedicellarias . 



a. Adambulacral armature : furrow series radiating, subpalmate ; 



actinal spines in a co-ordinated group . 



b. Adambulacral armature in longitudinal series parallel to the 



furrow. Post-adambulacral plates with fascioles 



b. Abactinal plates in oblique transverse rows on each side of the 



median series. With special internal imbricating ridges. 

 Actinal intermediate plates aborted or very few in number. 

 Pedicellariae present ........ 



a. Adambulacral armature Astropectinoid, with oblique median 

 series. Flattened squamiform spinelets on infero-marginal 

 plates .......... 



PARARCHASTERIN.fi. 



Pararchaster. 



Pontaster. 



PLUTONASTERIN.fi. 



Dyt aster. 



Plutonaster. 

 Lonchotaster. 



PSEUDARCHASTERINfi. 



Pseudarcliaster. 

 Aphroditaster. 



Abchasterin^e. 



A rchaster. 



