EEPORT ON THE CRINOIDEA. 289 



B. On the Characters of Young Pentacrinidce. 



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 Pentacrinidse 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 Metacriniis nodosus, some of which are 

 figured on Pis. XVIIL, XXXa., XXXY., 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 ; PI. XXX. fig. 1 ; PI. 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 Tvith a total length of 80 mm. (compare Pis. XXXV. and XXXVII.) ; 

 and the cup with its small basals presents a singular resemblance to that of Plicatocrinus 

 and Bathycrinus (PL VII. figs, 1-3, 6 ; PL Villa, 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 th-e absence of pinnules from the arm-bases. Hyocrinus 

 (PL VI.) is another type with high spade-like radials; but the basals are of the same 

 character, and not small and inconspicuous as in young Pentacrinidae and in Bathycrinus, 

 while the arms are totally dilferent. 



Another character of the incompletely developed Crinoid, which is very marked in 

 Rhizocnnus and Bathycrinus, and still more so in the aberrant Plicatocrinus and 

 Hyocrinus, is the comparative freedom of the second radials. In many Comatulse they 

 are closely united laterally ; while in most of the Palseocrinoids, as in Apiocrimis 

 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 Comatulaj. 

 But they are often in very close apposition, while in young individuals of the same 

 species they are comparatively free (Pis. XVIIL, XIX., XXIX., XXXa., XXXV., 

 XXXVIL). The arm-joiuts 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 XXXII. — 1884.) li 37 



