REPORT ON THE CRINOIDEA. 51 



primitively five or eight. Two instances in which Pentacrinus varies in the direction of 

 Mctacrinus have come under my notice. One is in Pentacrinus mulleri (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 joints in the ray. The first two above the primary radials are 

 united by a bifascial articulation, while the axUlary is a syzygy. I have elsewhere de- 

 scribed two specimens of Millericrinus pratti in which there are four radials, in one case 

 on two out of the five rays (Quart. Jouru. Geol. Soc, vol. xxxviii. p. 35, pi. i. fig. 23). 

 Similar variations occur among the Comatulse. 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 angidatus, 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 (PI. XII. 

 figs. 5-10 ; PI. XXXTX. fig. 1). The radials of Metacrinus angulatus, therefore, are 

 practically four in number, the second of which is a syzj'^gy and bears a pinnule like the 

 third. 



In Metacrimts 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 (PI. L. figs. 1, 6-16 ; PI. LI. fig. 1). 



In Encrinus, Extracrinas, and in most recent species of Pentacrinus, as also in a few 

 Comatulge (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 difi"erence 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 Pateocrmoids [Sitzmujsh. d. II. CI. k. baier. Akad. d. TViss., 1882, Bd. i. p. 105). 



