REPOET ON THE ASTEROIDEA. 181 



armature when contracted. The tube-feet have conical tips when extended, but which 

 appear slightly knob-like when contracted. 



No pedicellariaj of any kind are present. 



Colour in alcohol, a brownish grey over the paxillar area ; marginal plates and actinal 

 surface a bleached yellowish white. 



Young Phase. — In a small specimen from Station 203, measuring R = 22 mm., r= 6'5 

 mm., the number of marginal plates is twenty-four, and in general character this example 

 accords in all points with the adult form, the species being unmistakable. The remark- 

 able webbed fringes are fully developed, and the furrows between the marginal plates are 

 ver}^ wide. The number of spinelets in the paxillas and in the armature of the adam- 

 bulacral plates is rather less, especially on the attingent sides of the latter, as might 

 naturally be expected. The spinelets in the furrow series range in number from four to 

 six, according to position. On the larger paxillse of the disk seldom more than six to nine 

 marginal spinelets are present, and not more than one or two central granules ; along the 

 ray five or six appears to be the normal number. The madreporiform body is relatively 

 nearer the margin than in the adult form. The centre of the abactinal region is slightly 

 introverted as in many Astropectinidag. The development of the terminal (or "ocular") 

 plate is interesting. In the young stage referred to, the plate is divided along its entire 

 median line, forming a more or less wide and gaping channel, with the edges rounded, 

 along which the abactinal membrane passes and more or less aborted paxillar spinelets ; 

 beneath the membrane lies the terminal tentacle, there being no completion of the 

 calcareous ring on its abactinal side. In the larger example from this locality, a thin, 

 narrow, calcareous connection is developed on the floor of the furrow, but only at the 

 distal extremity of the plate, forming there a delicate arch over the terminal tentacle. 

 This division of the terminal plate is full of significance as regards the formation of this 

 so-called single plate. 



Variation. — In the specimen from Station 203 there is a small amount of variation 

 which is worthy of notice, although it might readily be passed over. This occurs in the 

 armature of the adambulacral plates, the prominent robust thumb-like spinelet on the 

 aboral margin of the plate being wanting (see PL XVIII. fig. 2). The largest example 

 is smaller than that from Hong Kong, hence it is possible that the " thumb" may be 

 developed only after full maturity is attained. On the other hand it may be said that 

 as the example under notice measures R = 37 - 5 mm., r = 9'75 mm., and has exactly the 

 same number of marginal plates (thirty-one, exclusive of the terminal) as the larger Hong- 

 Kong specimen, its normal adult characters may be considered to be present. 



On comparing the two forms it may further be remarked that the furrow series of 

 spines on the adambulacral plates are comparatively longer in the specimens from Station 

 203, and also that the breadth of the adambulacral plates in relation to their length is 

 slightly greater. The marginal spines are comparatively longer and narrower, and they 



