42 



Mr. W. K. Spencer. On the Structure and [Mar. 22, 



anal inter-radius has also produced the secondary fusion of radii 

 I and II, and IV and V, a phenomenon not confined to Agelacrinus, 

 but one found commonly in the Pelmatozoa. Jaekel (8, p. 8) has called 

 attention to this, "Diese Verschiebung der Gabelung zwei Strahlen findet 

 aber iiberall bei Pelmatozoen im analen Inter-radius statt, wo sich die 

 Primarporen, das Parietalseptum und der After zwischen zwei Strahlen 

 einschieben. Dadurch wird die Abgliederungsstelle der E/adien I 

 und V etwas nach den Seiten verschoben." The calcification of the 

 plates must be secondary to the location of the internal organs, for 

 these are formed first during ontogeny. Secondary symmetries in the 

 ambulacral plates are thus readily accounted for. 





f. P . 



FIG. 11. View 1 mm. removed or 40 sections ^ mm. thick. 



Fia. 12. View \\ mm. removed or 60 sections T l n mm. thick. 



