PLATE XVIII. 



Steeptelasma BOBtJSTUM (page 153). 



Figure 1. Side view of a nearly perfect specimen of this species from the Red River 

 valley in Manitoba, presented to the Museum of the Survey by the 

 Smithsonian Institution. 

 II la. Longitudinal section of the same, to shew the internal structure. 



Protae«a (vetdsta? var.) magna (page 155). 



Figure 2. Portion of the upper surface of a colony of this species, magnified three 

 times, to shew the shallow calices, wedge-shaped septa, and small 

 tubercles in the centre of each calyx. 



,1 3. Longitudinal section of a portion of a corallum of this species, magnified 

 eight times. 



n 3a. Transverse section of the same, also eight times the natural size. 



Stomatopoba Canadensis (page 161). 



Figure 4. ' Zoarium of the specimen described. 

 II 4a. The same, four times the natural size. 



