80 THE NAUTILUS. 
Potamolithus Rushii Pilsbry,n. sp. Uruguay River at Paysandu, 
Uruguay. 
Potamolithus Iheringi Pilsbry, n. sp. Uruguay River at Pay- 
sandu, Uruguay. 
Potamolithus microthauma Pilsbry, n. sp. Uruguay River at 
Paysandu, Uruguay. 
Potamolithus Hidalgoi Pilsbry, n. sp. Uruguay River at Pay- 
sandu, Uruguay. 
Potomolithus dinochilus Pilsbry, n. sp. Uruguay River at Pay- 
sandu, Uruguay. 
Potamolithus Buschii ‘ Dkr, Ffld. Uruguay River at Paysandu, 
Uruguay ; Rio de la Plata at San Gabriel’s Island. 
Potamolithus tricostatus Brot. Uruguay River at Paysandu, 
Uruguay. 
Potamolithus conicus Brot. Uruguay River at Paysandu, Uru- 
guay. 
Potamolithus Orbignyi Pilsbry, n. sp. Uruguay River at Pay- 
sandu, Uruguay. 
Potamolithus lapidum @Orb. Fray Bentos. 
Potamolithus lapidum v. supersuleatus Pilsbry. Rio de la Plata 
at San Gabriel’s Island. 
Potamolithus Sykesii Pilsbry, n.sp. Uruguay River at Paysandu, 
Uruguay. 
Potamolithus bisinuatus Pilsbry, n. sp. Uruguay River at Pay- 
sandu, Uruguay. 
Potamolithus bisinwatus v. obsoletus Pils. 
Potamolithus gracilis Pilsbry,n.sp. Uruguay River at Paysandu, 
Uruguay. 
Potamolithus gracilis v. viridis Pils. Uruguay River at Fray 
Bentos. 
CYRENIDZ, 
Corbicula limosa 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. 
Spherium sp. undet. Creek in the Prado, Montevideo. 
Pisidium sp. undet. «“ «“ «“ fe 
Pisidium sp. undet. “ «“ “ e 
UNIONID&. 
Unio parallelopipedon Lea. Rio de la Plata at Colonia, Uru. 
guay. 
