4 PEOCEEDINGS OF THE NATIOIs^AL, MUSEUM. vol. 63, art. 16. 



Type.— C?it. No. 346770, U.S.N.M. It measures: Length, 52 mm.; 

 height, 33 mm.; diameter, 28 mm. It comes from Colon, in the 

 Province of Entre Rios, Argentina, and was presented by Doctor 

 Felippone. This locality is nearly opposite the city of Paysandu, 

 Uruguay. This species classifies with Diplodon firmus Lea, to which 

 it bears a close relationship. It is shorter, higher, and very much 

 more inflated than firmus. 



EXPLANATION OF PLATES. 



PlATE 1. 



All figures slightly reduced. 

 Fig. 1. Diplodon podagrosus, new species, right valve. 



2. Diplodon podagrosus, new species, left valve. 



3. Diplodon (Bulloideusl) perfragilis, new species, right valve. 



4. Diplodon (Bulloideusl) perfragilis, new species, left valve. 



5. Diplodon podagrosus, new species, dorsal view. 



6. Elliptio herrerae, new species, right valve. 



7. Elliptio herrerae, new species, left valve. 



8. Elliptio herrerae, new species, dorsal view. 



Plate 2. 



All figurea slightly reduced. 

 Fig. 1. Diplodon {Bulloideusl) perfragilis, new species, left valve. 



2. Diplodon (Bulloideusl) perfragilis, new species, dorsal view. 



3. Diplodon (Bulloideusl) perfragilis, new species, right valve. 



4. Elliptio herrerae, new species, right valve. 



5. Elliptio herrerae, new species, left valve. 



6. Diplodon podagrosus, new species, left valve. 



7. Diplodon podagrosus, new species, right valve. 



Plate 3. 

 Elliptio herrerae, new species, right valve, enlarged. , 



