288 THE VOYAGE OF H.M.S. CHALLENGER. 



PL XXXVI.; PI. XXXVII. %. 22; PL XXXIX. figs. 4, 7-11 ; PL XLI. figs. 1-3, 5-8, 

 15-17 ; PL XLV. figs. 2, 4 ; PL XLVII. 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 pis. xiv.-xvii. 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, as in Pentacrinus naresianns and Pentaa'inus deconis (PL XXXa. fig. 6 ; PL XXXYL), 

 and in a less degree also in Pentaoinus miiUeri and Pentacrinus hlakei (PL XXXI. 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 XXVII. fig. 1), Pentacrinus wyville-thomsoni 

 (PL XIX. figs. 3, 4), and occasionally also in Pentacrinus asterius. But in these cases 

 the alteration of the supra-nodal joint is not very considerable. Among the Pentacrinus 

 species it is most marked in Pentacrinus ivyviUe-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 Pentacrinus miiUeri, Pentacrinus 

 maclearanus, Pentacrinus naresianus, Pentacrinus hlakei, and Pentacrinus decorus they 

 are directed downwards (Pis. XIV., XVL, XXVIIL, XXIX., XXXL, XXXIV.), and their 

 bases are received in the hollowed sides of the infi'a-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. ; PI XXXIX. fig. 9), Metacrinus 

 cingidatus (PL XL.), Metacrinus wyvillii (PL XL VIII.), Metacrinus costatus (PL XLIX. 

 figs. 1-3), Metacrinus interruptus (PL LIL), and Metacrinus tuberosus (PL LIII. 

 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 LIII. 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. 



' On Three New Species of Metacrinus, Trans. Linn. Soc. Land. (Zool.), ser. 2, vol. ii. p. 443. 



