BASAL PLATES IN CRINOIDEA CAMERATA 675 



In speaking of the base in the Flexibilia, Springer says : 



The posterior basal upon which it [the anal series] rests is excavated into a 

 sort of shallow socket, like the articulating face of a radial, on the right shoulder 

 of the plate, so that we will usually see a small tongue or angle of that plate 

 rising up to the left of the base of the anal plate higher than to the right; or, 

 if the socket-like excavation is not so plain as this, the upper edge of the basal 

 is distinctly sloped to the right. 1 



Furthermore, in Abacocrinus the writer has found a marked reduc- 

 tion of the right side of the posterior basal and a compensating 

 enlargement of the right-posterior basal (PI. II, No. 7). There is 

 here shown a marked tendency for the stimulus arising from the 

 developing intestine to inhibit the growth of the posterior basal 

 upon the right side and to permit the growth of the adjacent 

 right-posterior basal. 



Upon two of the accompanying plates (Pis. I, II) are illus- 

 trated the specimens upon which the evidence for sutural 

 reappearance through failure of anchylosis is based. These illus- 

 trations show clearly the appearance of the anterior suture in 

 Melocrinus, Actinocrinus , Steganocrinus, and Hexacrinus, and this 

 suture is so often represented that it cannot be ascribed to any 

 other cause. The appearance of this suture could only be accounted 

 for upon Wachsmuth and Springer's theory by plate splitting, a 

 supposition which is absolutely without foundation. It will fur- 

 thermore be noticed that in no instance do the posterior and right- 

 posterior sutures appear in the same specimen. Both sutures are 

 sometimes absent, but in general the posterior suture is present 

 and the right-posterior absent. The reappearance of the anterior 

 suture and the failure of the right-posterior suture to reappear in 

 any specimen in which the posteriorly directed suture is present, 

 and in which other combinations of lost and normal sutures do 

 appear, is the evidence upon which the theory of atrophy and 

 compensating hypertrophy is based, and is here submitted as 

 evidence that plate shifting such as Wachsmuth and Springer 

 assumed probably did not take place, but that the right-posterior 

 basal suture assumed a posterior position upon partial atrophy of 

 the posterior basal and compensating hypertrophy of the left side 



J Ref. 31, p. 496. 



