176 THE VOYAGE OF H.M.S. CHALLENGER. 
massive. Covered with hyaline, deciduous granules; devoid of spmes, excepting one 
adpressed, flattened, lateral spine on the infero-marginal plates. Deep, well-defined 
channels along the sutures between successive plates, the margins bordered with a 
webbed fringe formed of small spinelets enveloped in a continuous membranous invest- 
ment; the fringe continuous round the inner end of the supero-marginal plates. 
Abactinal area with paxille. Paxille with very massive basement plates, suboval 
internally, pedicle columnar, crown with one or more central eranules on the tabulum, 
surrounded by a marginal series of short spinelets, which radiate horizontally, and are 
united, at least in part, by a membranous web. 
Adambulacral plates superficially subquadrangular or rhomboid; the furrow margin 
with a series of short, subcylindrical spinelets, five or six in number, forming a small 
radiating comb; the other three margins bearing small, skin-covered, papilliform spine- 
lets, directed over a channel which intervenes between adjacent adambulacral plates, and 
also between the adambulacral and the marginal plates. Actinal area of the adambulacral 
plates covered with skin and devoid of spines. Ambulacral furrows entirely closed by 
the adambulacral plates and their armature, when contracted. 
Actinal interradial areas well developed, with a few large plates, regular and pave- 
ment-like in their disposition, covered with hyaline deciduous granules, each plate mar- 
gined with a webbed fringe like that on the marginal plates; well-defined channels along 
the suture lines of the plates. 
Superambulacral plates present. Tube-feet conically pointed. 
No anus. No pedicellariz. 
Remarks.—The type of this remarkable genus is the starfish to which Miller and 
Troschel gave the name of Archaster hesperus. Specimens, nearly all in a dry state, are 
to be found in the British Museum, as well as in several of the Continental museums, but 
the form has nevertheless been left in its anomalous position, although other observers 
have noted some of its remarkable characters. Under these circumstances I have given 
below an account in detail of its general structure. It will be seen to have nothing of 
generic import in common with the two other members of Miiller and Troschel’s genus 
Archaster, Archaster typicus and Archaster angulatus, or indeed with the other forms 
which have been hitherto ranked as Archaster. The presence of the superambulacral 
plates, the conical pointed tube-feet, the absence of an anus, and also the absence of 
pedicellarize, would seem naturally to associate this form with the Astropectinide, whilst 
the massive granulose plates, devoid of all spines excepting the lateral, with their singular 
marginal fringe, the character of the adambulacral plates and their armature, and like- 
wise that of the actinal intermediate plates, constitute a series of structures that isolates 
the form very distinctly from other genera at present known. 
