EEPORT ON THE CRINOIDEA. 253 



externally, and their upper and under faces approacli one anotlier rather sharply, owing 

 to the convexity of the upper surface of the basals, so that their inner ends are very thin. 

 The centre of the funnel which they form is occupied by the compact plug of close cal- 

 careous network which was mistaken by Sars for a basal rosette (PI. Villa, fig. 7 ; PL X. 

 figs. 1, 4 — hr). This is attached firmly to the inner ends of the radials, and comes away 

 with them. It lies on the top of the convex upper surface of the basals, the sloping sides 

 of which are divided into fossse for the reception of the radials. Close to the 

 inner end of each fossa is an elongated opening ; and there is a similar one at the 

 centre of the inner end of each radial ; but it is not exposed 

 until after the removal of the central plug. Ludwig's view, 

 however, requires that there should be an opening at the inner 

 lateral angle of each radial and none in the centre, as is reaUy 

 the case. The inference from this fact is that the primary 

 interradial cords actually fork in the basals, and that the left 

 branch of one fork, and the right branch of the next one pass 

 out together through one of the elongated openings on the 

 upper surface of the basal ring, which crosses the line of the fm. is.— Diagram of the distribution 



111 °^ "'^ axial cords in the calyx of 



interbasal suture. I find this to be actually the case. RUzocrinus lo/otensis. b, basais ; 



R, radials ; i', first brachials. 



Sections through the uppermost part of the basal ring, above 



the level of the chambered organ, clearly show the forking of the primary cords, 

 though no interradial lines of suture are visible at these points, as should be the 

 case on Ludwig's theory of the composition of the calyx. At the same time I can 

 readily understand how the use of the section-method alone led him to faU into this 

 error. For owing to the convexity of the upper surface of the basals, a horizontal 

 section through their central upper part might pass through the lowest and outer edge of 

 the radial pentagon, and thus show interradial sutures, although the central portion of 

 the section with the forking cords really belonged to the basals. The question is not a 

 very important one ; and but for my having been able to examine a dissected calyx, the 

 exclusive use of the section-method would have led me to follow Ludwig's description, ex- 

 cept in one point. He does not seem to have noticed the presence of the intraradial commis- 

 sures first described by himself in Antedon ; for he neither mentions them, nor introduces 

 them in his diagram and figures. The special interradial commissures are of course absent, 

 being unctionally replaced by the secondary interradial cords; but every two of these which 

 converge within the substance of a radial are united by an intraradial commissure, just as 

 they are in the Comatulse. This is clearly distinguishable in both the series of horizontal 

 sections which I have cut through the calyx of Rhizocrinus lofotensis (PI. Villa, fig. 6, ico). 

 The distribution of the axial cords in the calyx of Rhizocrinus is thus somewhat 

 difi"erent from that described by Ludwig, as will be seen if the accompanying woodcut 

 (fig. 18) be compared with fig. 18 on Taf. vi. of his memoir. 



