REPORT ON THE CRINOIDEA. 305 



himself under the name of Pentacrinus decorus. He was thus led to state that while the 

 two outer radials of Pentacrinus asterius are united by sj'zygy, those of Pentacrinus 

 miiUeri are articulated, a mistake almost the opposite of that made by Liitken. It is not 

 difficult to understand how Miiller's error arose ; for the line of syzygy is not dotted as it 

 is in the Comatulae, where the apposed faces are marked by radiating ridges. There is 

 little or nothing of this striation on the syzygial surface of Pentacrinus asterius (PI. XII. 

 figs. 18, 21) ; and the muscular unions of the remaining calyx- and arm-joints are so very 

 close that there is hardly any external character by which the syzygy between the two 

 outer radials may be detected. Its presence is evident enough between the two joints 

 following each axillary, as they are shorter than their successors. But nothing of this 

 kind appears in the case of the radials, and as they are very apt to become slightly 

 separated at the edges I have found it almost impossible, especially in dry specimens, to 

 determine the real nature of the union without separating the joints. This was done 

 by Sir Wyville Thomson, whose preparations are figured in PI. XII. figs. 15-25. 



The basals of Pentacrinus asterius are of very variable size, like those of Pentacrinus 

 decorus, though not to the same extent. They are sometimes small, rounded knobs, not 

 meeting one another upon the exterior of the calyx ; or larger and more prominent, 

 meeting their feUows in the re-entering angles beneath the radials ,' but they never form 

 a completely closed ring of triangular or pentagonal plates flush with the radials, as they 

 do in Pentacrinus wyviUe-thomsoni, Pentacrinus cdternicirrus, and some other species 

 (PL XVIII. figs. 1-3 ; PI. XIX. figs. 1, 6, 7 ; PL XX. figs. 2, 3; PI. XXV.). 



Liitken, Thomson, and others have endeavoured to establisli as one of the characters 

 of Pentacrinus asterius that the nodal joints of the stem are low and simple, while those 

 of Pentacrinus miilleri and Pentacrinus decorus are thick and double, consisting of two 

 parts united by syzygy. This is not really the case, however. In all recent Pentacrinidse 

 the nodal joints proper, i.e., those which are pierced by the canals lodging the cirrus- 

 vessels, are always single and united by syzygy to those next below them. But the line 

 of junction is sometimes so nearly obliterated as to be only visible with difficulty; while 

 in other cases, such as Pentacrinus asterius (PI. XIII. fig. 8), it is hardly distinguishable 

 from the ordinary junction lines between the internodal joints, which are crenulated 

 much less than usual. 



The following may therefore be regarded as the special marks of Pentacrinus asterius: — 

 a robust stem with long internodes and wide cirrus-sockets ; the ray-divisions rather 

 irregular in number and grouping ; the projections of the pinnule-joints. 



Little is known about the range of Pentacrinus asterius, either in depth or in space. 

 Examples have been obtained ofi" Barbados, Guadeloupe, Martinique, Montserrat, Nevis, 

 and Saba Island ; while the only two cases in which the depth is known with certainty 

 are respectively 120 and 320 fathoms. Like the three other West Indian species, it is 

 not known to occur out of the Caribbean Sea. 



(ZOOL. CHALL. EXP. PAET XXXU. — 1884.) 39 



