256 Annals of the Sjuth African Museum. 



specimens, the median, unpaired spine at the tip of the jaw is very 

 conspicuous in every case, so there is reason to believe it is nor- 

 mally present in the adult. The smallest specimen has R = 7'5 

 mm., r = 4'5 mm., R:=1'66r; the unpaired spine on the jaw is 

 perhaps '35 mm. long by -25 mm. thick. In the largest of the 

 young specimens, r = 5'5 mm. while R was certainly more than twice 

 as much; the unpaired jaw-spine is about -70 mm. long by '30 mm. 

 wide. There is no indication of spinelets on any of the inferomar- 

 ginal plates. 



MEDIASTER CAPENSIS *, sp. nov. 

 Plate XVI. Figs. 1, 2. 



R 53 mm.; r = 19 mm.; R = 2-8r. Br = 20 mm.; at middle 

 of ray, 8 mm. ; at tip, 2-5 mm. Disk large, somewhat swollen in 

 the radial regions ; arms wide at base, narrowing rapidly at first 

 and then, on distal half of arm, very gradually to the blunt tip. 

 Abactinal plates of disk and base of rays, tabulate, more or less 

 paxilliform, crowned with a marginal series of 12 15, slightly angu- 

 lar, blunt spinelets or coarse granules and within this circle 3 8 

 similar and scarcely smaller granules; in the interradial regions, 

 near the superomarginals and on the distal part of the rays, the 

 plates are less paxilliform and carry 5-10 small granules, variously 

 arranged ; occasionally one of the granules, on the larger plates, is 

 replaced by a small 2-jawed pedicellaria, but these are neither 

 numerous nor conspicuous. Papulae numerous, large, arranged quite 

 regularly, so that around each plate, there are six, but around any 

 two plates there are ten and around any four plates only sixteen. 

 Madreporite small, rounded triangular, about as large as one of the 

 larger abactinal plates, only half as far from centre of disk as from 

 disk-margin. 



Superomarginal plates about 29 on each side of each ray, all 

 wider than long, the interradial ones almost twice as wide as long; 

 they are closely covered with granules, almost exactly like those on 

 the adjoining abactinal plates; there are 50-60 granules on one of 

 the interradial superomarginals; occasionally a pedicellaria replaces 

 a granule. Terminal plates small, slightly swollen, almost circular 

 or rounded hexagonal. Inferomarginals apparently one fewer than 

 superomarginals on each side of each ray ; the series alternate more 

 or less clearly at least at the middle part of the arm; the covering 



* In reference to the geographical occurrence, the region being a new one for 

 the genus. 



