32 THE VOYAGE OF H.M.S. CHALLENGER. 



the Apiocrinidte and of so many of the Palfeocrinoids. The applied surfaces of the cylin- 

 diical 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 rido-es." 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 (PL Vc. fig. 4), and others have only slight indications of the striation. 

 But the radiating stripe never " resemble minute pores jienetrating the walls," as stated 

 by Wachsmuth and Springer," of the similarly marked joint-faces in the PaliBoerinoids. 



The stem of Hyocrinus is much more rigid than that of the BourgueticrinidsB. The 

 short cylindrical joints are united by uniformly disposed ligaments (PI. Vc. fig. 5, Is), 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 (PI. Vc. fig. 5, rs) of the same nature as those just described in the 

 Bourgueticrinidse (PL Vila. figs. 1, 2, rs). 



So far as I can make out from the only two fragments of stem which have reached 

 me, measuring 70 and 85 mm. respectively, there are a large number of discoidal joints 

 at the top of the stem (PL VL figs. 1-3). Theii- 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 in one example from 1 mm. to nearly 

 1'5 mm. -ttithin 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. 



' Journ. Linn. Soc. Loud. (Zool.), vol. xiii. p. 52, 1878. ^ Revision, part i. p. 14. 



