AND RELATED GENERA, SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 67 



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

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



Fig. 4a. 



Fig. 4b. 



Fig. 4c. 



Fig. 4d. 



FrGS. 4a-d. — Scheme to illustrate the origin of Rugosa, assuming that the development of the mesenteries to begin with 

 has proceeded as in the Endocoelactidse. The black tongues are endoccelic septa, the shaded tongues exocoelie septa. 



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

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



