PLATE IV. 



Amplexopora superba. (Pago 16.) 



Figure 1. Fragment of the zodrium. Natural size. 



" 1 a. Tangential section, enlarged about fifteen times. 



" 1 b. Portion of the same, enlarged about thirty times. 



** I c. Longitudinal section, enlarged about fifteen times. 



Amplexopora Canadensis. (Pago 17.) 



Figure 2. Fragment of the zoarium. Natural size. 



" 2 a. Tangential section, enlarged about fifteen times. 



" 2 b. Portion of the same, enlarged about thirty times. 



" 2 c. Portion of a tangential section from another specimen, similarly 

 enlarged to show more clearly the spiniform tubuli. 



" 2 d. Longitudinal section, enlarged about fifteen times. 



