REPORT ON THE CRINOIDEA. 291 
length of the joints does not increase in the same proportion ; and I am therefore not 
surprised at having met with but one individual in which the stem-joints are longer than 
wide, as shown in Pl. XXXV. fig. 1. 
A comparison of the figures on this plate, which represent the two youngest 
individuals dredged by the “ Blake,” with those of the older, but still immature forms 
figured in Pl. XXXVL, will show, however, that the great relative height of the stem- 
joints is a very characteristic feature in the development of Pentacrinus decorus. The 
same feature is apparent in Pentacrinus wyville-thomsoni (Pls. XVIII, XIX.), 
Pentacrinus naresianus (Pl. XXVIIL; Pl XXXa. fig. 1), and Metacrinus nodosus 
(Plobetis. 33 Pl Lidge), 
The sculpture on the terminal faces of these internodal joints of young individuals 
(Pl. XXXa. figs. 2,3; Pl. XXXVII. fig. 9; Pl. LI. figs. 2-5), as in the case of those 
intercalated between the pre-existing joints in other stems (PI. XXII. figs. 3-12; 
Pl. XXXVIL. figs. 10, 13, 14), is more or less obscure; but the petaloid markings are 
evident from the first, as might be expected. 
The external appearance of the nodal joints not unfrequently alters considerably 
during growth. Thus, for example, in Pentacrinus decorus the characteristic expansion 
down to the upper edge of the cirrus-socket (Pl. XXXVI.) scarcely appears at all in the 
young nodal joint (Pl. XX XVII. fig. 5); while in Pentacrinus naresianus there is a trace 
of this expansion in the young stem, though it entirely disappears in the adult. In 
Pentacrinus wyville-thomsoni, again, the overlap of the lower edge of the cirrus-socket 
above the infra-nodal joint is far less evident in the young stem (PI. XVIII. fig. 3) than 
it is in the adult (Pl. XIX. figs. 3, 4). In Metacrinus nodosus, however, the characteristic 
enlargement of the nodal joints between their cirrus-sockets is very evident in a young 
stem with relatively high joints (Pl. LI. figs. 6, 7). 
C. The Calyx and its Contents. 
The calyx, 7.e., the combined ring of basals and radials, is constituted in the same way 
in both the living genera of Pentacrinide, viz., Pentacrinus and Metacrinus, as is evi- 
dent from a glance at Pl. XII. The former may therefore be taken as the type; for it 
is the better known genus, and has a long geological history, while Metacrinus is not 
yet known to occur in the fossil state. The calyx of Pentacrinus, while more like that 
of ordinary Comatule, @.e., Antedon, Actinometra, and Eudiocrinus, than the corre- 
sponding part is in Rhizocrinus and Bathycrinus, nevertheless differs from it in a very 
important character. This is the presence of unmetamorphosed basals, such as are only 
found in Atelecrinus and Thawmatocrinus (Pl. LVI. figs. 1-4) among Comatule ; for 
the embryonic basals of the ordinary types undergo the well known transformation into 
a rosette. This structure covers in the chambered organ which is lodged within the 
