422 Reviews — Wachsmuth ^ Springer's Monograph on Crinoids. 



■were dealt with, to wit, 75 per cent. No amount of ingenuity- 

 could discover a proportion anything like this among Dicyclica 

 ]nadunata. I therefore afQrm " the extreme importance of these 

 points " with far greater confidence than in 1893, a confidence 

 strengthened by the nature of the criticism hitherto passed on 

 my views. 



That part of the dorsal cup below the radials may consist of 

 either one or two circlets of plates. The plates next below the 

 radials are called hasalia ; they alternate with the radials, i.e. each 

 basal is interradial in position. The plates that may occur below 

 these are called infrahasalia, and are radial in position. When 

 there are basals only, the base is said to be monocyclic ; when there 

 are also infrabasals, it is dicyclic. A monocyclic form with infer- 

 radials may appear to have a cup composed of three circlets ; but 

 these cannot be confused with the three circlets of a dicyclic form, 

 since inferradials do not alternate with radials proper as do basals. 

 Occasionally, it is true, the radials appear a little shifted to one 

 side, and it seems as though a continuance of such shifting might 

 render the inferradials indistinguishable from basals. Thus Dicyclica 

 might be derived from Monocyclica. A very obvious objection to 

 this view lies in the coexistence of basals with a radianal in 

 many Dicyclica, for the radianal is generally admitted to be 

 nothing other than the right posterior inferradial. That difficulty 

 could be overcome by denying the accepted homology ; but 

 there remains a more fundamental objection, which will be 

 understood from comparison of figures D and M in Fig. 1 : — 



Fig. \. — Course of axial nerve-cords in Dicyclic (D), Pseudomonocyclic (P), and 

 Monocyclic (M) Crinoids. 



These show the course of the axial nerve-cords in a dicyclic and 

 monocyclic form respectively. It will be seen that these cords, on 

 their passage from the nerve-centre called the chambered organ 

 (c.o.) to the arms, bear a definite relation to the plates of the cup. 

 If this relation held good in early Palgeozoic crinoids, as we have 

 reason to suppose, then I find it impossible to conceive of any 

 shifting of the lower part of R in Fig. M that should produce such 

 an arrangement as that shown in R and B of Fig. D. Therefore 

 I reject the hypothesis of the derivation of Dicyclica from Mono- 

 cyclica. That hypothesis is not discussed by Wachsmuth and 

 Springer ; in fact, they refuse to consider a somewhat similar 



