CHAP. XI. 



Bahia Blanca. 



32 5 



each other, I found several bones and a tolerably per- 

 fect head of the Megatherium. Some of the large 

 Volutas, though embedded in the gravel-bed (C), were 

 filled with the red mud, including great numbers of the 

 little recent Paludestrma australis. These three lower 

 beds are covered by an unconformable mantle (D) of 

 stratified sandy earth, including many pebbles of quartz, 

 pumice and phonolite, land and sea-shells. 



M. d'Orbigny has been so obliging as to name for 

 me the twenty species of Mollusca embedded in the two 

 gravel beds ; they consist of — ; 



1. Volutella angulata, d'Orbig. 



4 Voyage' Mollusq. and Pal. 



2. Voluta Brasiliana, Sol. 



3. Olicancilleria Brasiliensis, 



[d'Orbig. 



I. „ auricularia, do. 



5. Olivina puelchana, do. 



6. Buccinanopscochlidium,do. 



7. ,, globulosum, do. 



8. Colombella sertulariarum, do. 



9. Trochus Patagonicus, and var. 



of ditto, d'Orbig. 



10. Paludestrina australis, 



[d'Orbig. 



II. Fissurella Patagonica, do. 



12. Crepidula muricata, Lam. 



13. Venus purpurata, do. 



14. „ rostrata, Phillippi. 



15. Mytilus Darwinianus, 



[d'Orbig. 



16. Nucula semiornata, do. . 



17. Cardita Patagoaica, do. 



18. Corbula „ (?) do. 

 19.. Pecten tethuelchus, do. 



20. Ostrea puelchana, do. 



21. A living species of Balanus. . 



22. and 23. An Astraea and en- 



crusting Flustra, apparently 

 identical with species now. 

 living in the Bay. 



All these shells now live on this coast, and most of them 

 in this same bay. I was also struck with the fact, that 

 the proportional numbers of the different kinds appeared, 

 to be the same with those now cast up on the beach : 

 in both cases specimens of Voluta, Crepidula, Venus/ 

 and Trochus are the most abundant. Four or five of 

 the species are the same with the upraised shells on 

 the Pampas near Buenos Ayres. All the specimens 

 have a very ancient and bleached appearance, 1 and do 

 not emit, when heated, an animal odour ; some of them 



1 A Bulinus, mentioned in the Introduction to the ' Fossil Mam- 

 malia in the Zoology of the Voyage of the Beagle,' has so much 

 fresher an appearance, than the marine species, that I suspect.it 

 must have fallen amongst the others, and been collected by mistake. 



