318 



PALEONTOLOGY OF ILLINOIS. 



favorably with certain interzooecial vesicles which I have ob- 

 served in Ceriocava ramosa d'Orb., from the Cretaceous of 

 France. 



Fig. 7. a and 6, transverse and vertical sections of Prasopora lycoperdon Vanuxem, 

 showing the usual type of cystiphragms. c, vertical section of Prasopora affinis Foord, 

 showing the isolated cystiphragms. d, small portion of a zooecial tube of Amplexopora 

 robusta UL, showing a funnel-shaped diaphragm supposed to be a modified cystiphragm. 

 e and /, transverse and vertical sections of Ceriocava ramosa, d'Orb., showing, beside 

 the spinelets and peculiar wall- structure, two vesicles that are supposed to be homologous 

 with the cystiphragms. 



In the accompanying cut I have figured sections of this species 

 for comparison with sections of Silurian forms having cysti- 

 phragms. In the Cretaceous form the vesicles are sub-spherical 

 and may be attached to the zocecial wall, or suspended from 

 the radiating spinelets so as to hang apparently free in the 

 zocecial chamber. In the first instance they resemble the 

 isolated cystiphragms of Prasopora affinis Foord, in a marked 

 manner, and I do not think there can be any question that we 

 are dealing wish structures in every way homologous with 

 true cystiphragms*. 



* Since the above was written I have detected very similar structures in an unde- 

 termined species of Fistulipora from the Hamilton group of New York. 



