52 



SIR C. WYVILLE THOMSON ON NEAV LIVING 



joints, whicli are united to one another by a close syzygial suture, 



the applied surfaces being marked with a pattern of radiating 



grooves and ridges like those of so many of the fossil genera, and 



like those of the recent Fentacrini. The joints become short and 



very numerous towards the base of the cup. 



The head, including the calyx and the Fig. 3. 



arms, is 60 millims. in length. The cup 



consists of two tiers of plates only (fig. 3) ; 



the lower of these, which must be regarded 



as a ring of basals, is formed as in some of 



the Platycrinidae, of two or three pieces : it is 



dijBBcult to make out which with certainty ; 

 for the pieces are more or less fused, and the 

 junctions in the mature animal are some- 

 what obscure. The second tier consists of five 

 radials, which are thin, broad, and spade- 

 shaped, with a slight blunt ridge running 

 up the centre and ending in a narrow arti- 

 culating surface for an almost cylindrical 

 first brachial. The arms are five in number, 

 they consist of long cylindrical joints deeply 

 grooved within, and intersected by syzygial 

 junctions. The first three joints in each 

 arm consist each of two parts separated by 

 a syzygy ; the third joint bears at its distal 

 end an articuilating facet from which a 

 pinnule springs. The fourth arm-joint is 

 intersected by two syzygies, and thus con- 

 sists of three parts ; and so do all the suc- 

 ceeding joints ; and each joint gives off a 

 pinnule from its distal end, the pinnules 

 arising from either 'side of the arm alter- 

 nately. The proximal pinnules are very 

 long, running on nearly to the end of the arm; 

 and the succeeding pinnules are gradually 

 shorter, all of them, however, running out 

 nearly to the end of the arm, so that distally 

 the ends of the five arms and tlie ends of all 



the pinnules meet nearly on a level. This tj , ^Ti,- 



, •' Hyocnnus oetheUianus, 



IS an arrangement hitherto entirely un- Wy. T. 



known in recent Crinoids, although we have About four times the 



something very close to it in some species JJ^^"'-^^ ^i^*'" ^^^^^^^ 



