80 THE NAUTILUS. 



Potamolithua Riishli Pilsbry, n. sp. Uruguay River at Faysandu, 

 Urugua}-. 



Potamolithua Uierinyl. Pilsbry, n. sp. Uruguay River at Pay- 

 sandu, Uruguay. 



Potamolithua microthauma Pilsbry, n. sp. Uruguay River at 

 Paysandu, Uruguay. 



Potamolithua Hidalgoi Pilsbry, n. sp. Uruguay River at Pay- 

 sandu, Uruguay. 



Potomolithus dinochihts Pilsbry, n. sp. Uruguay River at Pay- 

 sandu, Uruguay. 



Potamolithus flnsehii ' Dkr.' Ffld. Uruguay River at Paysandu, 

 Uruguay ; Rio de la Plata at San Gabriel's Island. 



Potamolithus tricostatus Brot. Uruguay River at Paysandu, 

 Uruguay. 



Potamolithua con lens Brot. Uruguay River at Paysandu, Uru- 

 guay- 



Potamolithus Orbiyny! Pilsbry, n. sp. Uruguay River at Pay- 

 sandu, Uruguay. 



Potamolithua lajiidnm d'Orb. Fray Beutos. 



Potamolithua lujiiduin v. auperaulcotua Pilsbry. Rio de la Plata 

 at San Gabriel's Island. 



Potamolithua Sykexii Pilsbry, n. sp. Uruguay River at Paysandu, 

 Uruguay. 



Potamolithus bisinuatus Pilsbry, n. sp. Uruguay River at Pay- 

 sandu, Uruguay. 



Potamolithus bisinuatus v. obaoleius Pils. 



I'lilnmo/ith n.? i/raeilia Pilsbry, n. sj). Uruguay River at Paysandu, 

 Uruguay. 



Potamolithua yntrilis v. ririilis Pils. Uruguay River at Fray 



Bentos. 



CYKKNID.I;. 



Corbifiifd HmotM Maton. San Gabriel's Island. 



Corbicula coloniensis Pilsbry, n. sp. Rio de la Plata above Colo- 

 nia, Uruguay. A larger, more trigonal form than the preceding 

 species. 



Sphcerium sp. undet. ('reek in the Prado, Montevideo. 



Pisidium sp. undet. 



Piitliliitm sp. undet. 



UNIONID/E. 



Unio parallelopipedon Lea. Rio de la Plata at Colonia, Urn. 

 guay. 



