46 
HOLASCELLA EUONYX. 
curved, conic spines, 7-15 n long. The basal part of these spines is directed 
outward, slightly upward, and usually encloses an angle of 105°-102° with the ray. 
Their ends are bent downwards, towards the centre of the spicule. These spines 
are regularly arranged and, when four in number, form a regular cross. 
The small discohexasters (Plate 24 , figs. 10-12, 13b, 14b, 15-17; Plate 25 , 
fig. 13a) measure 38-44 n in total diameter. They have a centrum 3.3-4 n 
in diameter, from which six equal and regularly arranged main-rays arise. The 
main-rays are cylindrical, 6.5-9 n long, 1-1.4 n thick, and simply rounded off at 
the end. About 1 n below the end each main-ray bears a high frill, which appears 
as a round, subterminal, transverse disc 5-7 n in diameter. From the margin 
and the upper distal face of this disc very numerous diverging end-rays arise, 
which together form a short and broad bunch, at the distal end 19-25 n in diame- 
ter. The individual end-rays are, at the base, curved, concave to the continua- 
tion of the main-ray axis, and in their distal and middle-parts straight. They 
are 13 n long, throughout about 0.2 p thick, covered with exceedingly minute, 
recurved spines along their length, and crowned at the end with a verticil of 
similar but larger spines. These terminal spines together form a kind of end- 
disc, generally a little less than 1 n in transverse diameter. 
The large hemidiscohexasters and discohexadines are very similar and 
differ from each other only in that one of the main-rays bears two end-rays 
(Plate 25 , figs. 2-5, 10, 11) in the former, whilst all six main-rays bear only 
one end-ray in the latter. The large discohexactines measure 173-232 /x in 
total diameter, usually 194-215 id. Their six simple rays are fairly equal and 
regularly arranged, straight or slightly and uniformly curved, and sometimes 
just perceptibly abruptly bent at the point where the short basal part, which is 
the main-ray, passes into the long distal part, which is the single end-ray. The 
short basal (main-ray) part of the ray contains an axial thread 6-7 m long; 
6- 7 m is accordingly the length of the main-ray. The long distal (end-ray) 
part is destitute of an axial thread. The rays of the large discohexactines are 
95-110 /d long and thickened at both ends. They measure at the base 4.5-6 id, 
at the thinnest point, which lies somewhere near the middle of their length, 
2.4-5 /d, and at the distal end 5-6.5 ^ in transverse diameter. Along their 
length these rays are either quite smooth or bear a few minute, recurved spines. 
The end is crowned by a terminal verticil of usually five or six recurved spines, 
7- 12 ^ long, and 1.8-4 m thick at the base. These spines are conic, uniformly 
recurved and rather sharply pointed; together they form an exquisite anchor 
15-22 /d broad and 10-16 ^ high. 
