REPORT ON THE CRINOIDEA. 



313 



The disk is ouly partially visible, but seems to have a tolerably regular pavement of 

 small plates. Arm-groove exceedingly narrow, the ambulacral plates being limited to the 

 pinnule-bases. The pinnules have well defined covering plates with occasional faint 

 indications of side plates. 



Colour in spirit, browTiish- white. 



Xoca%.— Station 122, August 10, 1873; lat. 9° 5' N., long. 34° 50' AV. ; 350 fatjioms; 

 red mud. One specimen. 



Remarks. — The leading characters of this elegant species were well described by Sir 

 Wyville Thomson in The Atlantic. Its nearest allies are Pentacrinus miilleri (PL XIV.), 

 Pentacrinus ivyville-thomsoni (PL XVIII. fig. 1), and Pentacrinus alternicirrus 

 (PL XXV.), all of which it resembles very closely in the regularity and grouping of the 

 arm-divisions. The stem, however, is totally different from that of Pentacrinus wyville- 

 thomsoni with its long internodes, and the number of arms is also greater than is usually 

 the case in this species. Pentacrinus miilleri and Pentacrinus alternicirrus approach it 

 most closely, having relatively short internodes ; but the arrangement of the cirri on the 

 stem of the latter species distinguishes it at once. Pentacrinus maclearanus closely 

 resembles some specimens of Pentacrinus miilleri in the shape of the nodal joints ; but, 

 apart from the characters of the internodes, it is readily identified by the unusual 

 shortness of its lowest pinnules and the more rounded form of the joints in the later ones. 



The close approximation of the nodal joints, and the downward curvature of the 

 cirri, together with the slight downward extension of the basals and the grouping of the 

 arms, are of interest as recalling the Liassic Extracrinus hriareus. 



Only four cirri are present at one of the nodes, the fifth socket being totally absent. 

 This indicates a variation in the direction of Pentacrinus alternicirrus, which has only 

 two or three cirri at each node (PL XXVI. figs. 1-3). 



4. Pentacrinus wyville-thomsoni, Jeffreys (PL XVII. figs. 2-6 ; Pis. XVIII. -XXIV. ; 

 PL LVII. fig. 1). 



1870. PeMacrinus Wyville-Thomsoni, Jeffreys, Proc. Roy. Soc, 1870, vol. xix. p. 157. 



1872. Pentacrinus icyville-thmnsoni, Wyville Thomson, Proc. Roy. Soc. Ediii., vol. vii. p. 767; and The 

 Depths of the Sea, p. 444. 



Dimensions. 



Total length, ......... 24-00 cm. 



Longest stem, rounded off at seventh node. 



Shortest stem, lounded off at fifth node, 



Diameter of stem, 



Longest cirrus (nineteen joints), 



Diameter of calyx, 



Diameter of disk. 



Length of arm (seventy joints), 



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



Length of pinnule from middle of arm (twenty-one joints), 



(ZOOL. CHALL. EXP. — PART XXXII. 1884.) 



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