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REPORT ON THE CRINOIDEA. 51 
primitively five or eight. Two instances in which Pentacrinus varies in the direction of 
Metacrinus have come under my notice. One is in Pentacrinus miilleri (Pl. XV. fig. 2). 
The second and third radials are articulated, but the latter is an axillary with a syzygy, 
so that there are primitively four radials. In the other case (Pentacrinus decorus) there 
are seven primitive jomts in the ray. The first two above the primary radials are 
united by a bifascial articulation, while the axillary is a syzygy. I have elsewhere de- 
scribed two specimens of Millericrinus pratt: in which there are four radials, in one case 
on two out of the five rays (Quart. Journ. Geol. Soc., vol. xxxviii. p. 35, pl. i. fig. 23). 
Similar variations occur among the Comatule. In one Antedon that I have examined, 
one of the rays consists of five joints, the axillary being a syzygy ; while in individuals 
of two other species, the axillary rests directly upon its first radial, the second radial 
having remained undeveloped. When there are five radials in Metacrinus, as in Meta- 
crinus angulatus, the third and fourth bear pinnules; but the second does not, for it is 
united by syzygy to the third, and has lost its individuality as a separate joint (Pl. XII. 
figs. 5-10; Pl. XXXIX. fig. 1). The radials of Metacrinus angulatus, therefore, are 
practically four in number, the second of which is a syzygy and bears.a pinnule like the 
third. 
In Metacrinus nodosus, on the other hand, there are primitively eight radials, but 
besides the syzygy between the second and third, there is another between the sixth and 
seventh ; so that there are really only six joints, all of which except the first and last 
(axillary) bear pinnules, while the second and fourth have syzygies, and are as much 
single arm-joints as the third brachial or any other syzygial joint in the arm of Antedon 
rosacea (Pl. L. figs. 1, 6-16; Pl. LI. fig. 1). 
In Encrinus, Extracrinus, and in most recent species of Pentacrinus, as also in a few 
Comatulz (Actinometra solaris, Actinometra typica, &c.), the two outer radials and the 
first two joints beyond them are respectively united by syzygy. On the principle ex- 
plained above, each pair would therefore be considered as forming a single joint, so that 
the true third brachial (itself a syzygial pair) would come to be the second. This would 
involve our describing these forms as having but two radials, the axillary with a syzygy, 
and syzygies both in the first and in the second brachials. I think, however, that this 
would be misleading, and make the difference between this type and that of Antedon 
rosacea and Pentacrinus naresianus appear much greater than it really is. 
The presence of three radials is such an absolutely constant character in all the five- 
rayed Neocrinoids excepting Metacrinus and Plicatocrinus,' that the fact of the outer 
ones being united by syzygy and not articulated seems to me to be of minor importance; 
and I do not assign to it the same morphological value as the syzygial union of the third 
and fourth primitive brachials, in which the former loses its pinnule. No Crinoid with 
1 Zittel has described a six-rayed example of this genus, in which the first joint above the cup (called by him the 
first brachial) is axillary as in many Palocrinoids (Sitzwngsb. d. IL. Ol. k. baier. Akad. d. Wiss., 1882, Bd. i. p. 105). 
