ortmann: south American naiades. 453 



be sure of the identification. In consequence I have been compelled to introduce a 

 number of "new species," although I am afraid that some of them are not really 

 "new." But I must leave the task of making out their synonymy to others, who 

 have access to authentic material representing the older forms. It should also 

 be remembered that the introduction of new names is justified by the rules of 

 nomenclature, when an original description is insufficient to enable the species to 

 be recognized . 



General Remarks as to the Affinities and Geographical Distribution of 



THE South American Naiades. 



The earlier writers generally placed the South American forms in the old 

 collective genera, Unio and Anodonta, to which a kind of intergrading group, called 

 Monocondylcva, and certain specialized types, such as Hijria and Castalia, were 

 added. Von Ihering was the first to recognize that the South American "Ano- 

 donta," so-called, differs from the Anodonta of the northern hemisphere in important 

 characters, and that it is related to certain African forms, Muiela, Spatha, etc. 

 He calls this genus Glnbaris Gray = Anodontitcs Bruguiere. But he left the other 

 forms under Unio. For these Simpson (1900) used the name Diplodon Spix. In 

 my preliminary report on South American Naiades (Ortmann, 1911a, pp. 108, 120, 

 129, 130) I was able to show that Diplodon, as well as Hyria and Castalia, differ 

 anatomically from the Unionidce of the northern hemisphere, and that Von Ihering's 

 separation of Glabaris from Anodonta is fully justified and correct. I also found 

 that the genera Hyria, Castalia (= Tetraplodon) , and Diplodon, recognized by 

 Simpson as a peculiar group, but still placed with the Unionidce, are actually more 

 nearly allied to "Glabaris," and form with this a group, the family Mutelidce, which 

 should be divided into two subfamilies, the Hyriinoi and Mutelince, each with a 

 number of genera, the anatomy of many of which, however, was still unknown. 



Subsequent investigations brought out the fact that Simpson (1900) was cor- 

 rect in associating certain Australian Naiades with the South American Diplodon, 

 since I was able to show that D. austmlis has practically the same anatomical 

 structure as the South American Diplodon (Ortmann, 1912), but that it should be 

 elevated to the rank of a separate genus, Hyridella Swainson, admitted as a sub- 

 genus by Simpson. 



The systematic arrangement and geographical distribution of the families and 

 sul)families of the Naiades would thus be as follows: 



