682 HERRICK E. WILSON 



posterior basal by the anal plate, the anal plate having been 

 interpolated by portional migration in the space created by the 

 demand of the hind-gut for enlargement. 



5. The widening of the posterior basal upon interpolation of 

 the anal plate was bilaterally symmetrical. 



6. The quadripartite, hexagonal base resulted from the anchy- 

 losis of the anterior pair of basals in a hexagonal genus with a 

 pentapartite base. 



7. The posteriorly directed basal suture in the subequally, 

 tripartite and bipartite, hexagonal bases is the homologue of the 

 right-posterior basal suture in the pentapartite 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. 



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. 



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. 



10. The hexagonal, tripartite base of the Hexacrinidae resulted 

 from the interpolation of an anal plate by portional migration, 

 through shifting of the right-posterior basal suture to a posterior 

 position, and closure of the anterior and left-posterior basal sutures, 

 in a simple platycrinid with a pentapartite base. 



11. The bipartite, hexagonal base in the Hexacrinidae resulted 

 from interpolation of the anal plate by portional migration, shift- 

 ing of the right-posterior basal suture to a posterior position, and 

 closure of the right-anterior basal suture, in a platycrinid with a 

 pentagonal, unequally tripartite base. 



BIBLIOGRAPHY 



1. Agassiz and Pourtales. "Echini, Crinoids, and Corals," -Mem. Mus. 

 Comp. Zool., Harvard Coll., 1874. 54 pp., 15 cuts, 10 pis. 



2. Angelin, N. P. " Iconographia Crinoideorum in Stratis Suecia," Reg.- 

 Acad. Sci. Suecica, 1878. 32 pp., 29 pis. 



