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 Villa, 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 Villa, 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 Vllb. 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 j)rocesses. 



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 completel)^ 

 striated as in Comatula, or even partially so as m Pentacrinus (PL XII. figs. 7, 10, 18, 21 ; 

 PL XXI. figs. 1 c?, 2(i, 5 a ; 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 rawsoni from 

 the Azores (PL 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. 53, 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 aj^posed 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 



' Criuoides vivauts, pp. 15, 22. 



