REPORT ON THE CRINOIDEA. 



37 



basals of Bathycrimis is extremely close, and in old individuals no sutures are visible 

 externally (PI. VII. figs. 1, 2, 11 ; PI. Vila. figs. 12-14), though they appear in 

 transverse section (PI. Vllb. fig. 2) and also in young examples. I have never suc- 

 ceeded, however, in separating the plates from one another by the usual methods. 



The radials of Bathycrimis, on the other hand, are much less closely united. The}' 

 are thin plates in contact with one another by quite narrow sides (PL VII. figs. G, 6a). 

 Those of Bathycrimis aldrichianus were described l^y Sir Wyville Thomson as being 

 " often free ; but in old examples they also are frequently anchylosed into a funnel-shaped 

 piece."* All the specimens which I have examined arc in the latter condition, though 

 the plates are readily separable. But I do not think it possible that they could ever 

 be perfectly free as the other two radials are; and I have always found them to be 

 closely united by ligaments up to the level of the circular commissure (PI. Vllb. fig. 4, /), 

 though they become much more free near the top of the calyx (PI. Vllb. fig. 5). The 



Fig. l.—Promachocrinus kcrguelensis. Calyx, x 6. 



A. Side view, sliowing the alternation of the five primary radials with the five others, which are separated from the ceutro- 



dorsal by the rays of the basal star. B. Upper view, showing the interior of the central funnel formed by the radials. 



difference between the " free " and the " anchylosed " conditions is probably only due to 

 variations in the extent to which limestone is deposited around the fibres of the above 

 mentioned interradial ligaments. 



The difference between the basal and radial rings in the amount of lateral union 

 {i.e., in the distinctness of the sutures) between their component joints, which is more 

 or less evident in Hyocrinus, Bathycrimis, and Rhizocrinus, appears also in some fossil 

 Crinoids. Beyrich has pointed out ^ that in young individuals of Encrimis gracilis the 

 sutures between the basals are invisible, although those between the radials are distinct 

 enough ; and the same character has been noticed by Mr. E. Etheridge, jun., and myself 

 as occurring in the Palaeozoic Allagecrimis atistini.^ 



' Journ. Linn. Soc. Land. (Zool)., vol. xvi. p. 50. 

 ■■^ Ueber die Crinoiden des Muschelkalks, Berlin, 1857, p. 44. 



■' On Allagecrinu.s, the representative of a new family from the Carboniferous Limestone Series of Scotland, Ann. 

 and Mag. Nat. Hist, ser. 5, 1881, vol. vii. pp. 285-288. 



