116 STAUROCALYPTUS HAMATUS. 



(Plate 16, fig. 39c; Plate 17, figs. 5-8, 9b, 10b) measure 96-165 /x 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 m in 

 diameter, the oxyhexasters with more than two end-rays on all or some of the 

 main-rays 96-130 fi in diameter. The main-rays (and simple end-rays) enclose 

 angles of 90° with their neighbours. The simple rays are 54-84 ti long, 3-4.5 tx 

 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, A-ery oblique spines, which point backwards 

 towards the centre of the spicule. The proximal spines are the largest and attain 

 \ ix'm 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 n long, and 3-5.5 /x 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 n long and 2.5-4 n 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 straightrrayed spicules described above and the spicules with hook-like rays 

 to be described below. The transitional hemioxyhexaster represented (Plate 17, 

 fig. 4) measures 170 /z 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 



