Plate IV. 



From specimens in the author's collection. 



1. Saccoblastus tcoodmani, 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 ventricosusj n. s., lateral view. 



8. Saccoblastus Uneatus, lateral view. 



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

 other. 



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



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



