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 Pentaorinus wyville-thomsoni (Pis. XVIIL, XIX.), 

 Pentacrinus naresianus (PL XXVIIL ; PL XXXa. fig. l), and Metacrinus nodosus 

 (PL L. fig. 3 ; PI LL fig.. 1). 



The sculpture on the terminal faces of these internodal joints of young individuals 

 (PL XXXa. figs. 2, 3 ; PL XXXVIL fig. 9 ; PL LI. figs. 2-5), as in the case of those 

 intercalated between the pre-existing joints in other stems (PL 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 XXXVL); scarcely appears at all in the 

 young nodal joint (PL XXXVIL 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 

 Pentaci-iims 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. XVIIL 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). 



O. Tlie Calyx and its Contents. 



The calyx, i.e., the combined ring of basals and radials, is constituted in the same way 

 in both the living genera of Pentacrinidaj, viz., Pentacrinus and Metacrinus, as is evi- 

 dent from a glance at PL XII. The former may therefore be taken as the t}^e ; 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 Comatulse, i.e., Antedon, Actinometra, and Eudiocnnus, than the corre- 

 sponding part is in Rhizocrinus and Bathycrinus, nevertheless difi'ers from it in a very 

 important character. This is the presence of unmetamorphosed basals, such as are only 

 found in Atelecrinus and Tliaumatocrinus (PL LVI. figs. 1-4) among Comatulse ; 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 



