48 THE VOYAGE OF H.M.S. CHALLENGER. 
following joints being axillaries. This is in accordance with the nomenclature employed 
by Zittel, who speaks of the joint in Cupressocrinus, which is called “articulare” by 
Schultze, and ‘“‘second radial” by Roemer, as a “first brachial ;” while he only describes one 
series of radials in the five-armed Pisocrinus.* The developmental history of the plates 
also indicates elearly that the second and following radials are really arm-joints. For 
they commence as imperfect rings, which soon become filled up with lengthening 
fasciculated tissue, just as is the case with the stem-joints and later brachials. But the 
first radials, like the basals and orals, commence as expanded cribriform films; while the 
endogenous additions by which they are subsequently thickened are cribriform like those 
of the basals, and not fasciculated like those of the two outer radials and the following 
arm-joints. Messrs. Wachsmuth and Springer’ have been led by their study of the 
Paleocrinoids to the same conclusion, 7.e., that “the arms fundamentally commence with 
the second radials ;” although they find in practice that for purposes of description “ it is 
more convenient to regard the arms as commencing with the first free plate beyond the 
calyx.” In very many Neoerinoids with ten or more arms this would be the second 
radial ; and in the multiradiate Metacrinus (Pl. XXXVIII.; Pl. XLIII. fig. 2; Pl. XLVI.; 
Pls. XLVIII.—LIL.) this is actually a syzygial jomt with a pinnule on the epizygal just 
as in the simpler Hudiocrinus indivisus, but an axillary appears a few joints farther on, 
and the rays begin to divide. In the other Pentacrinidze, however, in Bathycrimus, 
Holopus, and in most Comatule, as well as in the fossil Hnerinus and Apiocrinide, the 
second joints above the primary radials are axillaries, and it is not till the second (or 
rarely the first) joints beyond these that pinnules appear. In all these types the axillary 
and the joint immediately below it are of the same width as the primary radials in the 
calyx. But in Marsupites and in many Paleocrinoids (Platyecrinus, Cyathocrinus, &c.) 
they are very-much smaller than the primary radials, just as the homologous joints are 
in Hyocrinus (Pl. VI.). 
The primary radials which form the upper part of the calyx are generally distin- 
guished as the first radials ; while the following joints, as far as the first axillary inclusive, 
are called the second, third radials, &c., though they are really only arm-joints as is shown 
by their bearing pinnules in Metacrinus (Pl. XII. figs. 6,8; Pl. XXXVIIL; Pl. XXXIX. 
Gos PLAKLU fig. 2) Pl XLV. figels PL XLVI ; Pl. GV fot Pie xe 
figs, 1,; 2\sP1. Ly figs..1, 8,10, 14,165 Pl U1. fig..1 ; (PL LIL digo), oisince, too; ibis 
very convenient for descriptive purposes to use different names for the different regions 
of the arms, I see no reason for altering the names by which these plates are generally 
known, provided that their real nature is not lost sight of. 
The conventional use of the term “radials” for the joints between the calyx and the 
1 Paleontologie, pp. 348, 349. 
2 Phil. Trans., 1865, p. 541, pl. xxvii. figs. 1, 3; Ibid., 1866, pp. 729, 742, pl. xli. fig. 1. 
3 Revision, part ii. p. 10. 
