PLATE XXI. 



Fig. 1. Discopora plicata var. spinigera \. Lorenz. 

 Zooecia and ooecia. 



Lepraliella contigua Smitt. 

 Zooecia with avicularia. 

 Zooecia with oral spines. 

 Spines. 



Ooeciferous zooecia. 

 Zooecia provided with pores. 

 Zooecia with apertures of different forms. 

 Avicularium. 

 Triangular mandible. 

 Aperture with oral teeth. 

 Zooecium with a mucronate peristome. 

 Ancestrula. 



Operculum showing the marginal ridges. 

 Smittina miimscula (Smitt) Nordgaard. 

 Zooecia and ooecia. 



Peristome of a zooecium with the avicularian cham- 

 ber, median tooth and the two peristomal triangular 

 plates. 



