254 THE VOYAGE OF H.M.S. CHALLENGER. 
There is another point in the anatomy of Rhizocrinus which is not brought out at all 
in the semidiagrammatic figure given by Ludwig (Taf. v. fig. 7). The second brachials 
(third radials of his nomenclature) are relatively much too small; but whether he pur- 
posely neglected the appearance presented by them, or whether they were really small 
and undeveloped in his specimens from reparation after injury, I cannot say. The whole 
of the visceral mass is occupied by the winding gut (Pl. VIIIa. fig. 8, G); so that the 
body-cavity is reduced to a minimum. But the outline of the visceral mass is not 
circular as represented by Ludwig, for a large diverticulum of the gut extends outwards 
between every two brachials. These approach one another over its outer end, so as to 
protect it, and it is supported on either side by one of the large processes bordering the 
ventral furrows of the brachials which were described and figured by Sars. This is well 
shown in the left hand portion of Pl. VIIa. fig. 8; while the right hand side shows the 
second brachials almost meeting one another over the interradial diverticulum of the 
rectum. The visceral mass and third radials of Bathycrinus present the same characters 
as seen in Pl. VII. fig. 4a, and Pl. VIIb. fig. 7, the first of which shows the great pro- 
cesses on the ventral face of the axillary radial. It would be interesting to determine 
whether the axillaries of Bourgueticrinus present similar processes. 
The syzygies of Rhizocrinus, at any rate in the lower parts of the arms, are slightly 
different in character from those of other Crinoids. The apposed faces are not completely 
striated as in Comatula, or even partially so as in Pentacrinus (Pl. XII. figs. 7, 10, 18, 21; 
Pl. XXI. figs. 1d, 2d, 5a; Pl. XXX. figs. 20, 21), as Sars has already pointed out in 
the case of Rhizocrinus lofotensis.. Neither, however, are they perfectly simple, as is 
sometimes the case in Pentacrinus (Pl. XXVI. figs. 5, 8; Pl. XXXVII. figs. 3, 4; 
Pl. L. figs. 6, 7, 12, 13). For there is an indistinct vertical ridge around the opening of 
the central canal of the hypozygal, resembling that of a bifascial articulation ; and this 
forks at its lower end so as to enclose a somewhat triangular pit into which there fits a 
corresponding process of the epizygal. The hypozygal faces which I have found to show 
this character most clearly are those of the first brachials of a Rhizocrinus rawson from 
the Azores (PI. X. fig. 8). It is less visible in the corresponding joints of the Havana 
_ specimen (Pl. X. fig. 6). It likewise appears, though less distinctly, on the first brachials 
of a specimen of Rhizocrinus lofotensis from Havana (Pl. X. fig. 1). Sars makes no 
reference to it in his description of this species, but the pit on the distal face of the first 
brachial is clearly shown in his Tab. iii. fig. 58, and also in a dorsal view (fig. 54). The 
backward projection on the second brachial of Rhizocrinus rawsoni is represented in 
Pl. X. fig. 19; while figs. 17 and 18 show the apposed faces of a syzygial union farther 
out on the arms, the backward process of the epizygal and the corresponding pit on the 
hypozygal being very distinct. 
A curious peculiarity which is presented by one of the Azores specimens of Rhizocrinus 
1 Crinoides vivants, pp. 15, 22. 
