PLATE XVIII. 



THE BRANCHIAL SAC. 



FIG. 



1. At:iili<i iK-itleata Alder, (p. 115) 



2. A. amoena sp. nov. (p. 117) 



3. A. plebeia Alder (p. 118) 



4. A. sordida A. & H. (p. 121) 



5. A. canina Miill. (p. 123) 



6. A. obliqua Alder (p. 125) 



7. A. seabra Miill. (p. 130) 



8. A. Normani A. & H. (p. 133) 



9. A. affinis A. & H. (p. 137) 



10. A. pustulosa Alder (p. 139) 



11. A. elliptica A. & H. (p. 141) 



12. A. pellucida A. & H. (p. 143) 



All the figures much enlarged, but reduced in various pro- 

 portions from Mr. Hancock's drawings. 



