176 THE VOYAGE OF II.M.S. CHALLENGER. 



massive. Covered with hyaline, deciduous granules ; devoid of spines, 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 paxillae. Paxillos with very massive basement plates, suboval 

 internally, pedicle columnar, crown with one or more central granules 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 disjiosition, 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 pedicellarise. 



Remarks. — The type of this remarkable genus is the starfish to which Miiller 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 sreneral 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 

 pedicellarise, would seem naturally to associate this form with the Astropectinidas, 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. 



