208 Br. F. A. Bather— The Base in the 



quinquepartite base, as in Ihnaoerinus, or quadripartite, as in 

 Xenocrinidae (Figs. 1, 5). For such bases it is the most simple 

 explanation ; but, since the pressure of the hind-gut was presumably 

 along the right posterior suture, one must admit the possibility of 

 this having pushed the posterior basal over to the left and necessitated 

 growth on its right side. This, as Mr. Wilson says (p. 669), is 

 " a question of directive controls which cannot be readily answered ". 

 I prefer, therefore, to leave the door open. 



" 6. The quadripartite, hexagonal base [our Fig. 5] resulted 



from the anchylosis of the anterior pair of basals in a hexagonal 



genus with a pentapartite base." 



Translated into phylogeny, this means that Mr. Wilson follows 

 Mr. Springer (1913) in accepting my derivation of Xenocrinidae 

 from Tanaocrinus (1898, 1900). 



" 7. The posteriorly directed basal suture in the subequally, 

 tripartite and bipartite, hexagonal bases [our Figs. 1, 6 & 9] is 

 the homologue of the right-posterior basal suture in the penta- 

 partite and quadripartite bases, which has shifted its position 

 through atrophy of the right half of the posterior basal and 

 a compensating hypertrophy of the left side of the right-posterior 

 basal." 

 The quadripartite base (hexagonal or pentagonal) always tends 

 towards symmetry in itself and in relation to the sagittal axis 

 (radial axis of Beyrich), so long as it remains quadripartite ; but any 

 fusion of its elements throws it out of symmetry with the sagittal 

 axis, and to regain the relation a shifting of one or more sutures is 

 required. Mr. Wilson argues that the fusion is of the posterior basal 

 with the one on its left, and from this his conclusion 7 naturally 

 flows. The evidence he adduces from an abnormal Steganocrimis 

 pentagonus shows that the posterior basal could, on occasion, fuse with 

 the one on its right. All the same his conclusion is to be accepted, 

 not so much for the reasons he gives, as for the more general one 

 that the right posterior suture is on the line of weakness or fluidity, 

 due to intestinal pressure. The exception in the single Stegano- 

 crimis just mentioned was facilitated by its strongly marked radial 

 pentamerism and by the relative smallness and solidarity of its base. 

 "8. The basal sutures lost through anchylosis are potentially 

 present in the basal cup, and liable to reappear in individual cases 

 of delayed anchylosis, but not as a phylogenetic character." 

 That is to say, there is no reversal of evolution. 



" 9. The tripartite, hexagonal base in the Batocrinidae resulted 

 from the appearance of the posteriorly directed basal suture (see 7) 

 in a quadripartite base, accompanied by closure of the anterior and 

 left-posterior basal sutures." 



This differs from Wachsmuth & Springer's interpretation (our 

 Fig. 6) by the fusion of plate 3 with 2 instead of with plate 4 ; 

 but it is not quite clear, for in a quadripartite base, on Mr. Wilson's 

 own hypothesis, the anterior suture is the one already closed (as in 

 our Fig. 5). All that happened was the fusion of the posterior and 



