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



9. Pentacrimis mollis, n. sp. (PL XXXIII. figs. 7-10). 



Dimensions. 



Greatest height of specimen (fig. 9), . . , . . . lO'OO mm. 



Least height (fig. 10), ....... 8-00 „ 



Diameter of calyx across the first radials, ..... 6'50 „ 



Diameter of disk, ........ 4r'75 ,, 



This is a very singular type, and it is witli much hesitation that I have referred it to 

 Pentacrinus ; for it differs considerably from this genus in the relative proportions of the 

 lower parts of the calyx, and its stem is entii-ely unknown. But on the other hand it pre- 

 sents no character which seems to me of sufficient importance to justify a generic separation. 



Its most obvious peculiarity is expressed in the specific name which I have applied to 

 it. The cup, radials, and lower arm-joints, which alone remain, are not formed of the 

 usual hard limestone found in most other Echinoderms. But, externally at any rate, 

 they are of a somewhat leathery texture, and yield readily to pressure, though there 

 appears to be a rather harder core within ; while some of the joints show traces of the 

 usual calcareous skeleton, and the disk is extensively plated (PL XXXIII. fig. 7). 



Nothing remains of the stem except three or four thin stellate joints immediately 

 beneath the calyx. The rays of the star are bent upwards considerably, and enclose in a 

 sort of cup the lower j)ortion of the basal plates with which they correspond in position 

 (PL XXXIII. figs. 8-10). There are no traces of broken ligament-fibres on the under 

 face of the lowest remaining stem-joint, and this would seem therefore to have been 

 the upper joint of a syzygial pair with its cirri as yet undeveloped. 



The basals which form an entirely closed ring are unusually high for a Pentacrinus, 

 but also of considerable width, so as to support the expanding calyx above them. Their 

 outline, so far as it can be seen, is irregularly quadi'ate, the two lateral edges approaching 

 one another somewhat rapidly until they disappear beneath the upturned stem-joints ; 

 while the upper edges meet at a very open angle. The basi-radial suture therefore has 

 five well marked depressions in which the radials rest, and five intervening elevations 

 which mark the middle lines of the basals. The radials are short and widely pentagonal, 

 sloping upwards and outwards at a considerable angle. They have a somewhat strongly 

 marked median ridge which starts from near the basi-radial suture, but disappears before 

 reaching their distal edge, as is well shown in fig. 8 ; and the distal edge itself is more or 

 less everted, while the dorsal ligament uniting the first and second radials is somewhat 

 prominent. The remaining radials and the lower arm-joints are only properly visible in 

 the anterior and left antero-lateral rays as shown in PL XXXIII. fig. 9 ; for the joints 

 of the other three rays are so shrivelled and contorted as to make their recognition a 

 matter of considerable difficulty. Their general aspect is somewhat diagrammatically 

 represented in PL XXXIII. fig. 10. 



