777 



The strong posterior radiating ribs which distinguish this spe- 

 cies from the preceding do not commence their formation at an 

 early period in the growth of the shell. The general surface 

 appears smooth to the eye, but, examined minutely, presents the 

 same character of zigzag striation, but much more faint and ob- 

 solete. 



Australia. 



SPECIES NOT IDENTIFIED. 



P. amygdalina, Sowerby, Pro. Zool. Soc. 1834. p. 47. 



P. bidentata, Gray, Annals, p. 2b. 



P. costellata, Lamarck, Anim. s. vert. 



P. discors, Sowerby, Pro. Zool. Soc. 1834. p. 46. 



P. flabagella, Lamarck, Anim. s. vert. 



LIST OF FIGURES IN PLATE CLXVI. 



{The figure after the Name refers to the number of the Species) 



Fig. 







Kg. 





1. 



P. 



Pkoladiformis, Lam. 1. 



13, 14. P. 



nivea, C/ieni. 7. 



2. 





cultellus, Des. 4. 



15.— 



chinensis, Des. 16. 



3. 





concinna, Sowb. 3. 



16, 17.— 



robusta, Sowb. 14. 



4. 





Dactylus, Sowb. 5. 



18, 19.— 



lithophaga, Retz. 12. 



5. 





cultellus, Des. 4. 



20. — 



bipartita, Des. 15. 



6,7. 





denticulata, Sowb. 6. 



21.— 



typica, Jonas, 13. 



8. 





elegans, Des. 9. 



22.— 



bicolor, Sowb. 18. 



9. 





solid a, Sowb. 11. 



23.— 



semilamellata, Lam. 17 



10. 





elliptica, Sowb. 10. 



24, 25. — 



divaricata, Cliem. 19. 



11. 





serrata, Des. 2. 



26.— 



lapicida, Chem. 20. 



12. 





gracilis, Des. 3. 







