REPORT ON THE CRINOIDEA. 
(09) 
© 
B. On the Characters of Young Pentacrinide. 
Young individuals of Pentacrinus are naturally rare, as is only to be expected. It 
is related, however, that on one occasion a large number of them of all ages and sizes 
were thrown up on the shore at Barbados after a gale; but unfortunately for science 
no one on the spot had knowledge enough to recognise the value of this extraordinary 
event, and a great opportunity, such as may never occur again, was therefore lost. 
Nevertheless the discovery that recent Pentacrinid flourish in great numbers on certain 
parts of the sea-bed, like their predecessors in the Liassic and Jurassic Seas, has brought 
about a considerable increase in our knowledge of their premature stages of growth. The 
dredgings of the ‘“ Porcupine,” Challenger, and “Blake” have yielded several young 
individuals of three Pentacrinus species and of Metacrinus nodosus, some of which are 
figured on Pls. XVITI., XXXa., XXXV., and LI. 
Like the young Comatula, they are all distinguished by the relatively great height of 
the first radials as compared with those of the adult, which are wider than high, often 
considerably so (Pl. XIX. figs. 1, 6, 7; Pl. XXX. fig. 1; Pl. XXXVII. figs. 1, 2; 
Pl. L. figs. 1, 5), while the radials of the young individuals are spade-like, to use an 
expressive term introduced by Sir Wyville Thomson. This is naturally most marked in 
the youngest specimen with a total length of 80 mm. (compare Pls. XXXYV. and XXXVIL.); 
and the cup with its small basals presents a singular resemblance to that of Plicatocrinus 
and Bathycrinus (Pl. VII. figs. 1-8, 6; Pl. VIIla. fig. 1). The little we know of the 
former, however, shows that it is a totally aberrant type, and the resemblance must 
therefore be considered as in great measure accidental and not as indicating any genetic 
relationship. But Bathycrinus is a decidedly embryonic form, as is shown by the length 
of all its three radials and the absence of pinnules from the arm-bases. /Hyocrinus 
(Pl. VL) is another type with high spade-like radials; but the basals are of the same 
character, and not small and inconspicuous as in young Pentacrinidee and in Bathycrinus, 
while the arms are totally different. 
Another character of the incompletely developed Crinoid, which is very marked in 
Rhizocrinus and Bathycrinus, and still more so in the aberrant Plicatocrinus and 
Hyocrinus, is the comparative freedom of the second radials. In many Comatule they 
are closely united laterally; while in most of the Paleocrinoids, as in Apiocrinus 
and Guettardicrinus, they are practically immovable, and enter into the composition of 
the body. The second radials of Pentacrinus, however, rarely show any traces of the 
lateral pits lodging interradial ligaments such as occur in many multiradiate Comatule. 
But they are often in very close apposition, while in young individuals of the same 
species they are comparatively free (Pls: XVIIL., XIX., XXIX., XX Xa, XXXV.,, 
XXXVIL). The arm-joints of most young Crinoids, as well as those in the outermost 
and growing parts of the arms of more mature individuals, are always distinguished by 
(ZOOL, CHALL. EXP,—PART XXXIL—1884,) hi 37 
