xll process-blocks a^'l> other illfstratiye figures. 



Page 

 Fig. o. Di.igram sliowing tlie retarded development in a species 



of Procerithium compared with the deyelopment of 



P. cf. ogerieni 306 



6. Diagram ilhistraiing the dcTelopment of two honioeo- 



luorphic gastropods of diif'erent descent 307 



7. Diagram illustrating transversal homoeomorphy 308 



Figs. 8 & 9. Procerithium (■ Exelissa'J c\.numismale 316 



Fig. 10. Frocerithiuiii suhfistulosum 320 



11. Procerithiiiiii tenuiornattcin, sp. nov 321 



12. Procerithium cf, tenvAurnatum 322 



13. Ceritliinella cf. covfusa 323 



14. Diagram showing the adult whorls of various species of 



Zygopleura .- 327 



15. Zygopletira deleta, sp. nov 328 



16. Zygopleura inida 329 



17. Zygopleura capricornu, sp. nov 329 



18. Zygopleura s'uhrugosa,^^. nov. ! 330 



19. Zygopleura cL tceniata ..;... 331 



20. Zygopleura semitecta 332 



21. Katosira transgressa, sp. nov 334 



22. Proma.thildia ibex 337 



23. Promathildia ligaturalis 338 



