32 THE VOYAGE OF H.M.S. CHALLENGER. 
the Apiocrinide and of so many of the Palzocrinoids. The applied surfaces of the cylin- 
drical joints, forming the lowest portion of the stem with which we are acquainted, were 
described by Sir Wyville Thomson * as “being marked with a pattern of radiating grooves 
and ridges.” There appears, however, to be a good deal of variation in this respect ; for, 
while some of the joint-faces have the radiating pattern very well developed, others are 
perfectly plain (PI. Ve. fig. 4), and others have only slight indications of the striation. 
But the radiating strie never “resemble minute pores penetrating the walls,” as stated 
by Wachsmuth and Springer,’ of the similarly marked joint-faces in the Paleeocrinoids. 
The stem of Hyocrinus is much more rigid than that of the Bourgueticrinide. The 
short cylindrical joints are united by uniformly disposed ligaments (PI. Ve. fig. 5, 7s), the 
fibres of which are all of equal length and not longest in the centre as in the oldest parts 
of the stem of Bathycrinus and Rhizocrinus. The ligamentous fibres at each end of the 
joint extend into its substance for about one-fifth of its length, so that the calcareous 
tissue is closer towards the ends than in the median parts of the joints. These contain 
radial spaces (Pl. Ve. fig. 5, rs) of the same nature as those just described in the 
Bourgueticrinidee (Pl. VIIa. figs. 1, 2, 7s). 
So far as I can make out from the only two fragments of stém which have reached 
me, measuring 70 and 85 mm. respectively, there are a large number of discoidal joints 
at the top of the stem (PI. VI. figs. 1-3). Their thickness gradually increases from 
above downwards, until they are about half as long again as wide. The length then 
diminishes again and the width increases, rising im one example from 1 mm. to nearly 
1°5 mm. within twelve joints. The lower joints thus become more discoidal again, like 
those some little way below the calyx. What they were in the stem-fragment, 170 mm. 
long, which is mentioned by Sir Wyville Thomson, I have no means of knowing. 
Neither are we acquainted with the nature of the actual base of attachment. 
1 Journ. Linn. Soc. Lond. (Zool.), vol. xiii. p. 52, 1878. ? Revision, part i. p. 14. 
