138 EURETE SPINOSUM. 



29, fig. 10). In the few hemioxyhexasters, however, in which the main-rays are 

 unequal, a corresponding irregularity is also observed in the end-rays (Plate 29, 

 fig. 12). The regularly disposed end-rays are conic, sharp-pointed, and covered 

 with minute, backwardly directed spines (Plate 29, fig. 14). In a few hemioxy- 

 hexasters with exceptionally thick lateral main-rays the regularly disposed end- 

 rays are reduced in length and terminally rounded. In the normal, regular 

 hemioxyhexasters the end-rays are 25-44 ii long, and 1.8-3.7 ^i thick at the base. 

 In the irregular forms the shortest are sometimes only 13 ix long. The central 

 end-ray of each group of three is straight throughout; the two lateral ones are 

 either also straight throughout (Plate 29, fig. 12) or, much more frequently, 

 straight only in their middle- and end-parts, but curved at the base, concave to 

 the central end-ray. The chords of the lateral end-rays enclose angles of 47-52° 

 with the central end-ray. 



Besides these regularly disposed end-rays other end- or branch-rays some- 

 times arise from the lateral main-rays. Occasionally one or two supernumerary 

 end-rays are added to the regularly disposed three. These additional end-rays 

 extend, like the latter, in the plane of the lateral main-rays. More frequently a 

 branch-ray is seen arising some distance below the end of the lateral main-rays. 

 These branch-rays extend more or less vertically to the plane of the lateral 

 main-rays, and are parallel to the apical rays. In size and spinulation the 

 supernumerary end- and branch-rays are similar to the regularly disposed end- 

 rays; they are, however, more frequently irregularly curved. 



The axis of each lateral main-ray is occupied by an axial thread (Plate 29, 

 figs. 14-17, 19). This terminates at the end of the main-ray and does not send 

 branches into the end-rays. The latter are destitute of axial threads. 



The scopules (Plate 29, figs. 1-8, 26a) are 140-288 m long. They consist of a 

 centrum, 3.8-7 m in diameter, usually 4-5 m, from one side of which arises a shaft, 

 and from the other arise four or, rarely, five or si>{ end-rays. The shaft is conic, 

 straight, or slightly curved, 115-261 n long, and 1.9-2.4 ^ thick at the base. 

 Near the distal end and often also near the base it bears minute spines. The end- 

 rays diverge distally and together form a brush-like verticil 9-18 /i broad at the 

 end. The individual end-rays are very slightly cur\'ed, concave to the continua- 

 tion of the shaft at the base, and nearly straight in their remaining part. They 

 are 20-44 fi long, 0.9-1.5 fi thick at the base, very slightly attenuated towards the 

 end, and densely covered with minute, backwardly directed spines. At the end 

 they bear a verticil of larger, recurved spines, which together form a kind of 

 terminal disc with strongly serrated margin (Plate 29, figs. 7, 8). 



