422 



SCIENCE. 



[N. S. Vol. I. No. 16. 



Mytilus platensis Orb. 



Mj'tilus exustus L (magellanicus Rve. 

 fide Dall.). 



Area Martensii Reel. 



Azara labiata Mat. 



Tagelus gibbus Spgl. (platensis Orb.) 



Macti-a patagonica Orb. 



*Mactra Dalli v. Iher. (M. BjTonensis 

 fide Dall). 



f Maetra riograndensis v. Thes. (M. isa- 

 belleana Orb. fide v. Martens). 



Cytberea rostrata Koch. 



An otolith of a Seifenoid fish, Micropogon 

 undulatus L., very common at Rio Grande 

 do Sul, and probably also in the La Plata 

 estuary. 



All these moUusks are common species 

 of the Atlantic coast of Uruguay and Ar- 

 gentina and most of them also from Rio 

 Grande do Sul. Only three of them are of 

 special interest, as not now found living in 

 these latitudes. 



Purpura hwmastoma L., still common on 

 the coast at Rio Grande do Sul, is, I beUeve, 

 not now known from the La Plata region. 

 D'Orbigny, Petit and other authors have 

 suggested that this species has been distrib- 

 uted through the agency of navigation. 

 It is therefore important to note that it 

 occurs fossil in America, as it does in the 

 European Tertiary. 



lAtorina flava King, common from the 

 West Indies to Santa Caterina, is not known 

 to occur at Rio Grande do Sul. 



Nassa polygona Orb. seems to have al- 

 most the same distribution as Litorina flava. 

 I use D'Orbigny 's name in default of the 

 complete synonymy. Prof, von Martens 

 considers it synonymous with N. polygonata 

 Lam. Hidalgo, treating it in extenso (Moll. 



* This seems to me different from the Chilian form. 



t A very common species on the coast at Eio Grande 

 do Sul, but probably undescribed. Prof, von Martens 

 named it M. imbelleana Orb., but this is a species 

 with the beaks more inflated and the valves not so 

 thick. Descriptions wiU be published elsevrhere. 



del viage al Pacifico, III., p. 39) regards it 

 as being the same as N. cinisctdus Reeve, 

 with antillarum Dkr. and sturnii Phil, as 

 varieties. So I prefer the name of D'Or- 

 bignj', as to the application of which there 

 is no doubt. 



These are, therefore, species once reaching 

 to the 35° of south latitude, which now do 

 not occur south of Santa Caterina or Rio 

 Grande do Sul. It is quite possible that 

 other species exist in the actual fauna which 

 are dying out. For example, Neritina mele- 

 agris Lam., found at Santa Caterina. It 

 occui'S also in the bay of Paranagua, but 

 onlj' in one locality, though formerlj' it was 

 much more common, being not rare in the 

 shell mounds of the Sambaquis. Dunker 

 ( Jahrb. d. Deutsche mal. Ges. 1875, p. 245) 

 says that N. meleagris is common at Monte- 

 video, but this seems to be an error, as 

 D'Orbigny, myself and others have not 

 found the species in the La Plata region, 

 either recent or fossil. 



It was the opinion of Darwin, shared in 

 part by Burmeister, that deep bays entered 

 long distances into the interior during the 

 Pampean formation, which for the most part 

 is due to the action of winds and fresh water. 

 To this I also agree. To such a gulf we 

 owe the existence of the marine shells. The 

 important facts discovered by Ameghino 

 give a new turn to the discussion of the 

 origin of the pampas 



As Dall has showoi that in Florida some 

 of the Pampean mammals occur in beds 

 covered hy marine pliocene limestone, there 

 cannot be anj^ doubt that the pampean for- 

 mation is in part of Pliocene age. It 

 seemed that with the important study of 

 Santiago Roth the pampas question might 

 be considered as settled, but the facts here 

 considered awaken doubts. It is quite pos- 

 sible that observations here brought together 

 may be increased with time and more and 

 more tend to modify the basis of our knowl- 



