NEW FOSSIL PEARLY FRESH-WATER MUSSELS FROM 

 DEPOSITS ON THE UPPER AMAZON OF PERU 



By William B. Marshall 

 Assistant Curator, Division of MoUusks, United States National Museum 



The United States National Museum has recently received some 

 fossil Naiads collected by Prof. Joseph T. Singewald, of Johns 

 Hopkins University, in deposits at the headwaters of the Upper 

 Amazon, Peru ; also another sending collected by Dr. Harvey Bassler^ 

 likewise from Peruvian deposits. The exact geological horizon from 

 which these shells were obtained has not been definitely settled to 

 date. Conrad ^ says, " It is not possible to state without doubt what 

 the relative stratigraphical position of this group may be, but if 

 all the species are extinct it can not be later than the Tertiary. The 

 Pleistocene origin of the group is at least very doubtful." None of 

 the species found in these deposits are living to-day. 



Associated with these mussels were large numbers of Anisothyris, 

 Isaea, Neritina, and other fossils, which are brackish-water forms. 

 It is quite possible that the Naiads were swept in to these deposits 

 from higher levels by floods, and thus came to be mingled with the 

 brackish-water faunas. These shells, therefore, argue for the existence 

 of bodies of fresh water at the time they were living at or near the 

 place where they were found. 



Until now only one Naiad has been described from the deposit, 

 namely, Anodon hatesii Woodward. As Anodon {=Anodonta) does 

 not occur in South America, this shell is probably an Anodontites 

 belonging in the family Mutelidae. The new species described herein 

 belong in the subfamily Hyriinae of the family Mutelidae and are 

 the first fossil species of that subfamily described from South 

 America. They are related to two genera, Diplodon and Hyria^ as 

 will be shown in the remarks under the new genus Prodiplodon. 



PRODIPLODON, new genus 



Pearly fresh-water mussels of the family Mutelidae with beak 

 sculpture resembling that of the genus Diplodon and also that of 



» Amer. Journ. Conch., vol. 6, p. 192, 1870. 



No. 2748.— Proceedings U. S. National Museum, Vol. 74, Art. 3. 



2607—28 1 



