nS 



MCMURRICH. 



[VOL. I. 



of which appears to have its longitudinal muscles on its endo- 

 coelic surface, while in the other they appear to be on the 

 exocoelic side. 



In order to show the arrangement of the directives more per- 

 fectly, as well as the relations of the mesenteries of the second 

 and third cycles, I give below a diagrammatic representation 

 of a transverse section of each of the specimens examined. 



D 



7 G 



A complete absence of all directives has been described by 

 Boveri ('93) for the genus Gyractis; and for the reception of 

 this form he has proposed an order Holactiniae, considering 

 the radial arrangement of the mesenteries which the absence 

 of the directives brings about, sufficient to warrant the separa- 

 tion of forms showing it from the "biradial >: Hexactiniae. 



