* 126 THE VOYAGE OF H.M.S. CHALLENGER. 
covered and converted into canals by what Beyrich calls “an inner epiphysis.”1 This was 
of no great thickness, and was therefore easily worn so as to expose the grooves beneath. 
In Apiocrinus, however, the basals were simply grooved for the reception of the 
bifurcating interradial cords, though the radials were pierced by canals as usual. 
Beyrich’ speaks of the arrangement of the canals being the same as in Encrinus, and 
de Loriol refers to the circular canal ;* but I have been unable to make out definitely 
whether any intraradial commissure were present or not. At any rate the type resembles 
Pentacrinus rather than Encrinus ; for there is only one opening on the distal face of each 
radial instead of two, and in correspondence with this only a single series of arm-joints. 
We know nothing respecting the distribution of the canals in the calyx of the 
Bourgueticrinide, but the course of the axial cords in Rhizocrinus is somewhat different 
from that of Apiocrinus, and this is still more the case in Bathycrinus. The basals of 
Rhizocrinus are of considerable height (Pl. IX. figs. 1-3; Pl. X. figs. 2, 3; Pl. LUI. 
figs. 7, 8), and the primary interradial cords of greater length than usual; but they are 
completely enclosed in canals, and bifureate immediately beneath the synosteal surface 
on which the first radials rest. The two limbs of each fork are very widely separated, 
turn off horizontally, and form themselves the interradial portion of the circular 
commissure, instead of proceeding directly onwards through the radials, as their fellows 
do in Pentacrinus (Pl. XXIV. figs. 8, 9, av). The two secondary cords which enter the 
small radial are immediately united just within its imner face by an intraradial 
commissure (Pl. VIIIa. fig. 6, c.co), and then proceed onwards towards the single opening 
on the distal face (Pl. X. figs. 1-4). The above description differs in some points from 
that given by Ludwig, who took an entirely erroneous view with respect to the basals of 
this type, and failed to find the intraradial commissure. The subject is discussed more 
fully in the anatomical account of the genus (pp. 249-252). 
A still simpler condition than that of Rhizocrinus is presented by the aberrant genus 
Bathycrinus. The basals are low and the radials high (Pl. VII. fig. 2; Pl. VIIIa. fig. 1), 
exactly the reverse of what we meet with in Rhizocrinus (Pl. IX. figs. 1-3; Pl. X. 
figs. 2, 3; Pl. LIII. figs. 7, 8). The primary interradial cords (Pl. VIIb. figs. 2, 3, az) 
do not fork within the basals, as is usually the case ; but they pass upwards between every 
two radials, the sides of which are grooved for their reception (Pl. VII. fig. 6a). At the 
level of about half the height of the radials the primary cords divide, and the two branches 
of each pass off right and left into the radials, where they form an interradial commissure, 
from the angles of which the axial cords of the rays proceed (Pl. VIIb. fig. 4, c.co); while 
the two converging portions of the interradial commissure within each radial are united by 
an intraradial commissure just as in Rhizocrinus. The principal difference between the two 
types is that the primary interradial cords of Rhizocrinus fork within the basals, while 
those of Bathycrinus pass upwards between the radials, and then turn off laterally within 
1 Op. cit., p. 22. 2 Op. cit., p. 21. 3 Paléont. Frang., op. cit., p. 313. 
