Annals of the South African Musenm. 



dose coat of granules, among which are scattered irregularly a 

 number of spiniform grains; there are 75-100 of the nearly spheri- 

 cal granules to each square millimeter of surface: the spiniform 

 grains are 3-4 times as high as thick, pointed and well-spaced. 

 Radial shields narrow, widely separated, only the distal tip visible. 

 Upper arm-plates large, in contact basally but soon becoming slightly 

 separated; they are broadly triangular, with slightly convex sides 

 but the shape is variable owing to the degree of convexity of the 

 proximal sides; some or all of the basal plates have these sides so 

 strongly convex that they are almost bell-shaped and are nearly as 

 long as wide. In the holotype however most of the upper arm- 

 plates are distinctly triangular with a convex distal margin. Inter- 



Fig. 1. Upper side of part of disk and arm of Ophiacantha nerthepsila sp. nov. 

 Some of the arm-spines removed. X 10. 



brachial areas below, and margin of disk both radially and inter- 

 radially covered by overlapping scales, which are quite bare and 

 entirely free from granules. Genital slits wide but short, reaching 

 from the oral shields not quite to the second series of arm-spines. 

 Oral shields diamond-shaped, twice as wide as long; madreporite 

 much bigger than the others, its length and breadth more nearly 

 equal. Adoral plates large, quadrilateral, in full contact interra- 

 dially, about equally wide at the two ends, but the proximal margin 

 longer than the distal. Oral plates small and ill-defined but each 

 bears 4 (or 3) small, ilat oral papillae; these are twice as wide as 

 long, the outermost is distinctly the widest and bluntest; one or 

 more of the others may be pointed. There are 6 teeth in each 

 column, the lowest one or two pointed and somewhat triangular but 



