252 THE VOYAGE OF H.M.S. CHALLENGER. 
intérieur ou aminci des radiales, on remarque & chacun d’elles un petit trou rond, 
dow sort un sillon droit et lineaire (fig. 43, s), qui longe la ligne médiane de la face 
supérieure ou ventrale de chaque article et continue son parcours en remontant aussi de 
long du milieu de la face ventrale des radiales suivantes.” This interior truncated 
portion of the radials is really their ventral face; while the openings at its central 
portion are the ends of the axial radial furrows descending to the lower part of the 
calyx, and the furrows proceeding outwards from them are the ventral radial furrows 
(Pl. VIlla. fig. 7; Pl. X. figs. 1, 4—v7f) as described and figured by Sars, though 
Ludwig took them for interbasal sutures, Sars’s fig. 42 is particularly instructive in 
this respect, as four out of the five first brachials are i situ, and their ventral furrows 
are seen to be continued downwards on to the radials. 
The ventral interradial furrows which are so marked on the upper aspect of the calyx 
of many Comatule are absent or but slightly indicated in Rhizocrinus. Traces of them 
may be seen, however, in fig. 42 on Tab. 11. of Sars’s memoir. But the adjacent muscle- 
plates of every two contiguous radials are intimately fused and also slightly everted. 
Each is separated from its fellow on the same radial by a well marked, ventral radial furrow; 
and the united halves of the inner faces of adjacent radials thus assume somewhat the 
appearance of isolated interradial plates resting within and against the outer faces of 
the radials. Ludwig was thus led to consider them as basals, and so to fall into exactly 
the same kind of error with regard to their genetic relations as he attributed to Sars. 
I have nothing to add to his account of the chambered organ ; but his description of 
the cords which proceed from its fibrillar envelope needs a little modification. He has 
pointed out that they are interradial and not radial as described by Sars; but he says 
that they “ verbinden sich dann in den untersten Radialien durch Commissuren, ohne dass 
vorher eine Gabelung stattgefunden hitte.” Were this really the case, Rhizocrinus would 
be a much more anomalous form than it actually is. For in all other Crinoids, recent or 
fossil, in which this point has been worked out, with the exception of Bathycrinus, the 
primary interradial cords fork within the basals, and there are two openings either on the 
inner (Comatule) or on the under face (Pentacrinus) of each first radial (Pl. XII. 
figs. 11, 22; Pl. XX. fig. 9). Ludwig, however, figures these cords * in Rhizocrinus as 
single so long as they remain within the basals (top stem-joimt, Ludwig); and he believes 
them to fork in the suture between two radials, so that their branches would not enter 
the radials through their inner or under faces, but at their lower lateral angles. 
This is not quite the case, however, and it is probably to be explained by Ludwig's 
having used the section-method only, without attempting to separate the pieces of the 
calyx. This operation is one of no little difficulty, and some of the radials are sure to be 
fractured in the process ; but others separate from the basals along the sutural lines, and 
the arrangement of the canals can then be seen. The radials are comparatively low 
1 Zeitschr. f. wiss. Zool., Bd. xxix. p. 72, 1877, Taf. vi. fig. 18 
