AND RELATED GEN'ERA, SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 259 



As we see, the development of the Rugosa type may be explained by a similar 

 development of the mesenteries as in Halcurias or Porponia, though with the 



Fiu. 4A. 



FIG. 4B. 



FIG. 4c. 



FIG. 4D. 



Flos 4A-D. -Scheme to illustrate the origin of Rugosa, assuming that the development of the mesenteries to begin with 

 has proceeded as in tl.,- Eudocuilactid*. The black tongues are endocoelic septa, the shaded tongues exoccehc septa. 



difference that the development of new mesenteries is continued in the entloco3ls, and 

 that in each quadrant a suppression of mesenteries on the dorsal side takes place in each 



(ROY. soc. EDIN. TRANS., VOL. i,., <J7.) 



