Platk IV. 



From specimens iu the author's collection. 



1. Saccoblastus woodmani, lateral view. 



2. Same, base view. 



3. Saccoblastus obliquatus, lateral view. 



4. Same, base view. 



5. Saccoblastus wortheni, lateral view. 



6. Saccoblastus pyramidalis, lateral view. 



7. Saccoblastus ventricosus, n. s., latei'al view. 



8. Saccoblastus lineatus, lateral view. 



This row of figures shows the gradual development from one species to the 

 other. 



9. Pentremites serratus, from Ste. Genevieve, Mo. 



10. II. Pentremites t^dipaformis, n. s., lateral and basal views. 



