312 



THE VOYAGE OF H.M.S. CHALLENGER. 



Pentacrinus decorvs (PL XXXIV. fig. 2), is far less complete than in Pentacrinus 

 asterius. There is no trace of the large polygonal plates on the perisome between the 

 rays which we find in the latter species (PL XIII. fig. 1), and those on the ventral sur- 

 face of the disk are small and scattered, often being mere granules. The ambulacral 

 skeleton too is imperfectly developed. The covering plates of the pinnules do not rest 

 upon distinct side plates, but only upon an almost undiff"erentiated limestone band 

 (PI. XV. figs. 8, 9 ; PL XVII. fig. 9). 



3. Pentacrinus maclearanus, WpHille Thomson, 1877 (PL XVI. ; PL XVII. fig. 1). 

 1877. Pentacrimis madearanits, Wyville Thomson, The Atlantic, vol. ii. pp. 123-126. 



Di<me7\sions. 



Total length {fide C. W. T.), 



Length of stem, rounded off at twelfth node, 



Diameter of stem, 



Longest cirrus (twenty-five joints). 



Diameter of calyx, . 



Length of arm (sixty-eight joints). 



Length of pinnule on first free brachial (ten joints), 



Length of pinnule from middle of arm (fifteen joints), 



13-00 cm. 

 34-00 mm. 



5-25 „ 

 28-00 „ 



9-00 „ 

 80-00 „ 



7-00 „ 

 14-00 „ 



Description of an Individual. — Stem short and pentagonal, with rounded angles, 

 terminating below at the twelfth, node. The internodes consist of only one or two 

 comparatively thin joints. Nodal joints thicker, with enlarged and j^rominent angles ; 

 the cirrus-sockets, occupying almost their whole height, are cii-cular or slightly oval in form, 

 with a well-defined rim which extends dowTiwards on to the infra-nodal for a variable 

 distance. The cirri consist of twenty to twenty-five stout joints of tolerably equal size, 

 with a small terminal claw and no opposing spine. luterarticular pores scarcely visible. 



Basals rhomboidal, just in contact laterally, and extending slightly downwards over 

 the ujipermost stem-joints. Rays and their subdivisions in close lateral contact, the 

 joints as far as the tenth or twelfth brachial having flattened sides. The two outer 

 radials united by syzygy. Primary and secondary arms each of two joints also united by 

 syzygy. Total number of arms thirty-one, i.e., usually six to each ray in the foUowing order 

 — 2, 1 ; 1,2; palmar axillaries being generally developed only on the two outermost of the 

 four secondary arms. A tertiary axillary in one ray. The two lower brachials united by 

 syzyg}^, the epizygal bearing a pinnide. No other syzygies on the arms, which consist of 

 about seventy short and wide, oblong joints, overlapping very sHghtly at the base. 



The lowest j)innules are much shorter than their successors, and have only ten or 

 twelve joints, the basal ones being trihedral and the outer ones flattened. The middle 

 pinnules much longer, with about fifteen more rounded joints. 



