Plate IV. 



From specimens in tlie author's collection. 



1. Saccoblastus xooodmani, lateral view. 



2. Same, base view. 



3. Saccoblastus ohliqimtns, lateral view. 



4. Same, base view. 



5. Saccoblastus wortheni, lateral view. 



6. Saccoblastus pyramidalis, lateral view. 



7. Saccoblastus ventricosus, n. s., lateral view. 



8. Saccoblastus lineatus, lateral view. 



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

 other. 



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



10. 11. Pentremites tulipaformis, n. s., lateral and basal views. 



