210 Br. F. A. Bather — The Base %n the 



suture reappearance in the bipartite base show the potential presence 

 and position of all but the rigbt-posterior suture." One of these 

 examples (Wilson's plate vii, fig. 10) shows left posterior, anterior, 

 and right anterior sutures, which last does not accord with the 

 enlargement of the right anterior basal (3 -f- ) imagined by 

 Wachsmuth & Springer. The two other examples show a suture 

 in the anal interradius, and why the hypothesis demands that this 

 should have been shifted back to the right posterior radius I do not 

 understand. Mr. Wilson also objects, as before, that the anterior 

 basal suture "lost through anchylosis" cannot reappear. But it is 

 only Mr. Wilson who has supposed that suture to be lost ; 

 Wachsmuth & Springer thought it was shifted ; and to claim that 

 it could not shift back is to ride "the irreversibility of evolution" 

 a little too hard. Perhaps Mr. Wilson is bothered by Wachsmuth & 

 Springer's added element x, but, as already said, I think he attaches 

 too much importance to a diagrammatic mode of expression. 

 However, let us look at his own interpretation (having first 

 corrected another unfortunate misprint). He derives the Dichocrinus 

 base (Fig. 9) from one of Platycrinid plan (Fig. 2), by fusion of the 

 left compound basal (5 -f 1) with the small (left anterior) basal (2), 

 accompanied by a shifting of the right posterior suture into the anal 

 interradius, in line with the unmoved anterior suture. Granted the 

 antecedent conditions, this is certainly a simpler explanation, though 

 Mr. Wilson does not say how he reconciles it with his own views as 

 to the right posterior suture in abnormal individuals. In choosing 

 between the two interpretations we must be guided by the phyiogeny, 

 and here Mr. Wilson claims that the earlier examples of Dichocrinus 

 have a flexible tegmen more readily to be derived from that of an 

 early Platycrinid than from the "ridged tegmen" [?" rigid"] of 

 Hexacrinus. This seems a fair argument, and in this case plenty 

 of Silurian and Devonian genera are known that could be thus linked 

 up with Dichocrinus. If Mr. Wilson's interpretation of Dichocrinus 

 be accepted, then, whatever be the interpretation of Hexacrinus, it 

 will follow that the two genera evolved along independent lines. 



Such are the main theses of this interesting paper ; but there are 

 subsidiary matters that call for comment. 



In saying that Wachsmuth & Springer are the only writers who 

 have undertaken a general treatment of the subject, Mr. Wilson is 

 hardly fair to H. E. Beyrich, whose well-known paper " Ueber die 

 Basis der Crinoideabrachiata " 1 finds no place in his " Bibliography ". 

 If Mr. Wilson has not studied that paper he has not been fair to 

 himself either. Allusion has already been made to some of its 

 broader conceptions, here overlooked ; and, to descend to a detail, 

 Mr. Wilson would have learned from it that the plan of base which 

 he has discovered in some specimens of Melocrinus from Missouri, was 

 described by Beyrich as normal for JH. hieroglyphicus. 



In his account of plate-growth (pp. 501, 502) Mr. Wilson suddenly 

 breaks away from sentences with a strangely familiar ring to state 

 that the plates, after they have come into contact, increase in size 



1 Mbnatsber. Akad. Wiss. Berlin, February, 1871, pp. 33-55. 



