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



covered and converted into canals by what Beyricli calls "an inner epiphysis."' This was 

 of no great thickness, and was therefore easily worn so as to expose the grooves beneath. 

 In Ajnocrinus, 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 E^icrirms, 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 tj^je 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 

 Bourgueticrinidse, but the course of the axial cords in Rhizocrinvs is somewhat different 

 from that of Apiocrimis, and this is still more the case in Bathycrinus. The basals of 

 RMzocrinus are of considerable height (PI. IX. figs. 1-3 ; PL X. figs. 2, 3 ; PL LIII. 

 figs. 7, 8), and the primary interradial cords of greater length than usual ; but they are 

 completely enclosed in canals, and bifurcate 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, ar). The two secondary cords which enter the 

 small radial are immediately united just within its inner face by an intraradial 

 commissure (PL Villa, 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 stUl simpler condition than that of Rhizocrimis is presented by the aberrant genus 

 Bathycrinus. The basals are low and the radials high (PL VII. fig. 2 ; PL Villa, 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 Vllb. figs. 2, 3, m) 

 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 ^^■hich the axial cords of the rays proceed (PL Vllb. 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 

 ty|)es is that the primary interradial cords of Rhizocrinus fork within the basals, whUe 

 those of Bathycrinus pass upwards between the radials, and then turn off laterally witliin 



1 Op. cit., p. 22. 2 02). cit., p. 21. ^ Paleoiit. Frang., op. cit., p. 313. 



