ortmann: south amekican naiades. 569 



from Anodonliks, the former beinj^ characterized by a speciaHsation of the foot; 

 the latter by a speciahsation of the branchial opening. Mycetopoda is also peculiar 

 in having the anal opening closed above. We can express this in the following 

 diagram : 



Mycetopoda Leila 



Anodontitcs 



1 

 ? 



Iheringella, Fossula, Monocondyliea 



The anatomy furnishes no additional help for the understanding of the phyl- 

 ogenj^ of these genera, except the i)oints mentioned in the key. In fact, the anatomy 

 is so disappointingly similar in all of them, that it is practically useless. Only 

 in Mycetopoda and Leila have we been able to recognize higher stages of develop- 

 ment in the anatomy, but it should be mentioned that I have not been able to 

 verify this fact in Leila, of which I have not had the opportunity to examine soft 

 parts. The same is true of Iheringella. Of Fossula, Monocondijla;a, and Ano- 

 dontites, I know^ the anatomy very well, but no differentiations whatever have 

 been observed. 



The Species of South American Mutelin^. 



Genus Iheringella Pilsbry (1893). 



Pilsbry, 1893, p. 30; Simp.son, 1914, p. 1392. 



Characterized by rather broad hinge-plate and compressed or stumpy pseudo- 

 cardinals, two in the right and two in the left valve, the anterior pseudocardinal 

 of the left valve the most anterior of all hinge-teeth. These teeth, however, are 

 rather variable. 



This genus approaches the Hyriiiuc most closely in its hinge, but in the details 

 of its structure it is very different from any of them. It belongs to the La Plata- 

 drainage, and possibly also to that of the upper Amazon. 



41. Iheringella balzani (Von Ihcring) (1893). 



Plagiodon balzani Von Ihering, 1893, p. 69, PL 3, fig. 2. 

 Iheringella balzani Simpson, 1900, p. 914; 1914, p. 1359. 



Type-locality. — Rio Paraguay, near mouth of the Rio Apa, Matto Grosso, 

 Brazil. 



Neiv Locality. — Rio Paraguay, San Luis de Caceres, Matto Grosso, Brazil 

 (J. D. Haseman coll., May 25, 1909). Two complete shells and one left valve. 



