116 
STAUROCALYPTUS HAMATUS. 
(Plate 16 , fig. 39c; Plate 17 , figs. 5-8, 9b, 10b) measure 96-165 m in diameter 
and have from one to four end-rays. The forms with partly simple and partly 
bifurcated rays, that is the hemioxyhexasters with two end-rays on the branched 
main-rays, appear to be the most frequent. The true oxyhexasters usually 
have two or three, rarely three or four end-rays. The size of the spicule is, on 
the whole, in inverse proportion to the number of end-rays. The oxyhexactines 
and the hemioxyhexasters and oxyhexasters with two end-rays are 110-165 /x in 
diameter, the oxyhexasters with more than two end-rays on all or some of the 
main-rays 96-130 n in diameter. The main-rays (and simple end-rays) enclose 
angles of 90° with their neighbours. The simple rays are 54-84 n long, 3-4.5 n 
thick at the base, and conic. Their end is very slender and they terminate in an 
exceedingly fine point. The basal part of the ray is for a short distance smooth. 
Farther on it bears slender, straight, very oblique spines, which point backwards 
towards the centre of the spicule. The proximal spines are the largest and attain 
1 ix in length. Farther on they rapidly become smaller and on the distal part of 
the ray no spines at all can be detected. This decrease of the size-of the spines 
towards the ray-end is either gradual throughout, or there is a step-like, abrupt 
decrease a short way up. The rays of these spicules, particularly those in which 
there is such an abrupt decrease of the size of the spines, resemble the threads of 
exploded cnidoblasts of certain hydroids. I consider these simple rays as main- 
rays with a single end-ray; their proximal smooth part is their main-ray, their 
middle and distal spined part, their end-ray. The main-rays which bear end- 
rays are smooth and very short, only 4-8 /x long, and 3-5.5 m thick. The end- 
rays arise very steeply, often nearly vertically, from the main-rays and at once 
curve outwards, so that their nearly straight distal and middle-parts enclose 
angles of 30-35° with the continuation of the main-ray axis. Apart from their 
basal curvature these end-rays resemble in shape and spinulation the middle 
and distal spined part of the simple rays above described. The end-rays are 
spined quite down to the base, are 37-75 /x long and 2.5-4 /x thick at the base. 
Rarely hemioxyhexasters are met with some rays (end-rays) straight and 
others hook-like (Plate 17 , fig. 4). These spicules appear as transitions between 
the straight-rayed spicules described above and the spicules with hook-like rays 
to be described below. The transitional hemioxyhexaster represented (Plate 1 7, 
fig. 4) measures 170 ix in diameter, has two hook-like simple rays, two straight 
simple rays, and one main-ray with two straight end-rays. 
The oxyhexactines with hook-like rays (Plate 16 , fig. 39d; Plate 17 , figs. 1-3, 
10c) measure 140-227 m in diameter. The rays of the same spicule may be equal 
