EEPOKT ON THE ASTEROIDEA. 159 



The armature of the adambulacral plates consists of proportionally larger spines than 

 in the adult, and these are conical and pointed, and radiate apart, as in other forms of 

 Hyphalaster, instead of forming the almost straight uniserial line noticed in the adult 

 of Hyphalaster hyalinus. The terminal plate is thick and blunt at the end. 



If this really is the young form of Hyphalaster hyalinus it is extremely interesting to 

 note (1) up to what a comparatively late stage of growth the embryonic planting is re- 

 tained ; and (2) that these large plates entirely disappear and do not become metamor- 

 phosed into other plates, but give place to the very minute and simple spiniferous 

 TJiyonidium-like spicules which pervade the whole of the then delicate semi-transparent 

 abactinal membrane. 



Locality. — Station 274. In the Mid-Pacific, due north of the Society Islands 

 and due west of the Marquesas Islands. September 11, 1875. Lat. 7° 25' 0" S., long. 

 152° 15' 0" W. Depth 2750 fathoms. Radiolarian ooze. Bottom temperature 35°'l 

 Fahr. ; surface temperature 80 o- 2 Fahr. 



Remarks. — This species is distinguished from all the others by its remarkably delicate 

 structure, the abactinal membrane appearing at first sight merely like a semi-transparent 

 bag, by the mouth-plates bearing secondary spines, and by the two innermost super- 

 marginal plates on each side of the interradial line bearing small spinelets. 



2. Hyphalaster diadematus, Sladen (PI. XXI. figs. 1-4; PI. XXVIII. figs. 17-20). 



Hyphalaster diadematus, Sladen, 1883, Journ. Linn. Soc. Lond. (Zool.), vol. xvii. p. 237. 



Rays five. R = 24 mm. ; r = 10 mm. R < 2 - 5 r. 



Marginal contour stellato-pentagonal. Rays well developed, slender, springing from 

 the disk with a gradual taper, which is continued to the extremity ; the upper surface of 

 the ray arched rather than rounded. Abactinal surface of the disk slightly inflated above 

 the level of the marginal plates, and with a prominent conical peak in the centre of the 

 area. The minor radius is in the proportion of 41 "6 per cent. Interbrachial arcs well 

 rounded. 



The abactinal area is covered with a thick integument, uniformly beset with well- 

 spaced pseudo-paxillae, which are very small and regular, each composed of three or four 

 spinelets, those with the latter number being by far the most numerous. The paxillse do 

 not extend along the rays, but are confined to the actual disk-area ; a blank space is thus 

 left at the base of the rays, which has the appearance of being closely plated with small 

 round scales imbedded in the integument. In the neighbourhood of the conical peak the 

 paxillce become very small and crowded. Around this as a centre, and at some little dis- 

 tance away, a number of larger paxillae made up of more spinelets are arranged ; these are 

 congregated with more or less regularity into round groups, of which, roughly speaking, 

 there is one opposite the median line of each ray, with a smaller group intermediate 

 between each of the larger ones. The larger groups consist of ten to twelve large paxillae of 



