6lO PATAGONIAN EXPEDITIONS: ZOOLOGY. 



Rio Negro: Marsh of San Xavier (d'Orbigny); 12 leagues from Chichi- 

 nal (Roca Exped.). 



Genus DIPLODON Spix. 

 DIPLODON PATAGONICUS (d'Orbigny). 



Unio patagonica d'Orb., Voyage dans 1'Amer. Merid., p. 610, pi. 70, figs. 

 1-4. 



Rio Negro. 



DIPLODON FRENZELLII (Ihering). 



Uniofrenzelliiv. Iher., Archivfiir Naturgeschichte, 1893, p. 3, pi. 4, fig. 12. 



Rio Negro. 



It may be well here to correct the nomenclature of an allied genus of 

 the La Plata and Amazon basins, formerly known as Castalia Lam., 1819. 

 This name was believed to be preoccupied by Savigny, in Vermes, and 

 Tetraplodon Spix, 1827, has been substituted for it. 



The late Professor Eduard von Martens wrote to me under date of 18 

 Oct., 1893, as follows : " Concerning Castalia, the date of Savigny 's genus 

 of Annelids is given as 1817 in Agassiz's ' Nomenclator,' it is true, but I 

 am not sure that this is correct. I find Savigny's genus first in his Sys- 

 tem of Annelids, which is said to have been published in 1820, whereas 

 Castalia Lamarck was published in 1819, vol. V, part I, of Lamarck's first 

 edition [of the Animaux sans Vertebres\. 



" P. S. I have consulted in these days the original edition of L. Agas- 

 siz's Nomenclator and I find concerning Castalia the note : 



" ' Castalia Sav., Syst. annelid., 1817. Savigny Systeme des Annelides, 

 presente a 1'Acad. des Sci. en 1817, public en 1826.' 



"It is true that there is also an edition of the same work, in folio, 

 which makes part of the large ' Description de 1'Egypte,' and to which in 

 Engelmann's Bibliotheca Zoologica, vol. I, p. 581, the date 1820 is given. 

 By general consense the date of publication and not the date of finishing 

 a manuscript and presenting it to a learned body is accepted as fixing the 

 priority. I come to the conclusion that Castalia Lam., 1819 can stand 

 for the shell, and Castalia Sav. among the Annelids is to be changed." 



