288 THE VOYAGE OF H.M.S. CHALLENGER. 
Pl. XXXVI; Pl. XXXVII. fig. 22; Pl. XXXIX. figs. 4, 7-11; Pl. XLI. figs. 1-3, 5-8, 
15-17; Pl. XLV. figs. 2,4; Pl. XLVIL figs: 1-9; Pl. XLIX: figs. 3=5). 
The same characters may be seen in the numerous Pentacrinus joints figured in 
Tabs. 97-99 of the Encriniden, and on pls. xiv.—xvil. of de Loriol’s Swiss Crinoids. 
In some of these fossil joints the number of ridges at the sides of the petaloid figures 
may sometimes reach eight or ten; but the inner ones always meet their fellows in the 
interpetaloid spaces, while the outer ones appear externally. This is not the case in 
Extracrinus, which has a more extensive but smaller crenulation at the sides of the linear 
petals, as pointed out already (ante, p. 276). 
In the recent species of Pentacrinus the cirrus-socket may extend downwards below 
the articular surface so as to encroach very considerably on the internodal joint beneath 
it, asin Pentacrinus naresianus and Pentacrinus decorus (Pl, XX Xa. fig. 6; Pl. XXXVI), 
and in a less degree also in Pentacrinus miilleri and Pentacrinus blakei (Pl. XXXL. fig. 3); 
or the joint above the node may be slightly incised to receive the upper part of the 
socket, as in Pentacrinus alternicirrus (Pl. XXVIL. fig. 1), Pentacrinus wyville-thomsoni 
(Pl. XIX. figs. 3, 4), and occasionally also in Pentacrinus asterius. But m these cases 
the alteration of the supra-nodal joint is not very considerable. Among the Pentacrinus 
species it is most marked in Pentacrinus wyville-thomsoni (Pl. XXII. fig. 17). With the 
exception of those on the lowest nodal joint the cirri of this type are often found directed 
upwards (Pl. XIX. fig. 1), while in others like Pentaerinus miilleri, Pentacrinus 
maclearanus, Pentacrinus naresianus, Pentacrinus blake, and Pentacrinus decorus they 
are directed downwards (Pls. XIV., XVI., XXVIII., XXIX., XXXI., XXXIV.), and their 
bases are received in the hollowed sides of the infra-nodal joints. 
On the other hand, the tendency of the cirri of Metacrinus is to take an upward 
direction, the supra-nodal joints being slightly incised to receive their bases. This is well 
shown in Metacrinus angulatus (Pl. XXXVIII.; Pl XXXIX. fig. 9), Metacrinus 
cingulatus (Pl. XL.), Metacrinus wyvillii (Pl. XLVIII.), Metacrinus costatus (Pl. XLIX. 
figs. 1-3), Metacrinus interruptus (Pl. LII.), and) Metacrinus tuberosus (Pl. LIIL. 
figs. 1,2). In some species, such as Metacrinus varians (Pl. XLIV.), this character is not 
very prominent ; but it can be traced with more or less distinctness in all the species of 
the genus that I have seen, and is therefore (as far as it goes) of considerable value in 
the separation of Metacrinus from Pentacrinus, as in the case of Metacrinus tuberosus 
(Pl. LIL figs. 1-6) and Metacrinus stewarti,’ of which only the stems are known. But 
I have been unable to apply it to the determination of any fossil species, as this point is 
naturally but rarely illustrated in sufficient detail in the figures of Quenstedt and 
de Loriol. 
1 On Three New Species of Metacrinus, Trans. Linn. Soc. Lond. (Zool.), ser. 2, vol. ii. p. 443. 
