PLATE XI. 



Perigonimus vestitus, Perigonimcs minctus, Perigonimus serpens. 



Fig. 



1. Perigonimus vestitus, magnified. 



2. The same, natural size, extending over the surface of a Buccimim shell. 



3. Planoblast of same, shortly after liberation, and in the act of swimming. 



4. Perigoniwus mimdus, magnified. 



5. The same, natural size, attached to the operculum of Turritella communis. 



6. Planoblast of same, shortly after liberation. 



7. Perigonimus serpens, magnified. 



8. The same, natiu-al size, on a fragment of Plumularia. 



9. Planoblast of the same, shortly after liberation, and seen while swimming. 



