1896.] NATURAL SCIENCES OF PHILADELPHIA. 397 



easterly direction from tbe Gulf of Panama, and another from a 

 southeasterly direction from the Peruvian coast. Both are strong 

 currents, both have doubtless contributed their aid in populating 

 the Galapagos, but in this the Panama current seems to have pre- 

 dominated, not only because it has a shorter traverse, but because 

 around the Gulf of Panama and on the banks of the rivers falling 

 into it, a luxuriant fauna and flora are found close to the sea, while 

 along the Peruvian coast only in time of freshet could any large 

 quantity of debris be expected to reach the waters of the current, 

 owing to the aridity of the immediate shores. The two currents join 

 forces at some distance eastward from the islands, and pour through 

 the passages between them with considerable force. Professor Alex- 

 ander Agassiz has shown how much terrigenous material the Panama 

 current bears, and that there is no reason to doubt that trees still 

 bearing leaves and with some of their branches above water might 

 be carried from the Gulf and cast upon the islands, and that, at least 

 during the rainy season and in favorable years, there would be op- 

 portunities for animals so carried, especially land shells glued by the 

 epiphragm to the bark of branches, to gain vegetation on the shores 

 where they could support life and propagate their kind. Though 

 unproven, yet there can be little doubt that in this way the land 

 mollusk fauna of the islands was introduced and preserved.^ 



The first explorer^ of the Galapagos Islands for land shells was 

 Hugh Cuming, about 1830, who collected Bidimuhcs nux Brod., B. 

 utsiulatus Sby., and B. unifasciatiisShj., on Charles Island ; B. rugi- 

 ferus Hve., B. calvus Sby., and B. jacobi Sby., on James Island ; 

 while from his collection at a later time were described B. eschari- 

 ferus Sby., B. rugulosus Sby., B. verrucosus Vfr., B. nucula Pfr., and 

 B. galapaganus Pfr., without definite reference to a particular 

 island. Assuming that the last three mentioned were collected by 

 Cuming and not obtained from later collectors, this comprises eleven 

 species. 



The next collection was made by Darwin in 1835, who obtained 

 Buliviulus Daru'ini Pfr., B. sculpturatus Pfr., a Helix (not named 

 or subsequently reported for over half a century but, perhaps, 

 Trochomorpha Bauri) and thirteen other species not specified at the 

 time, as well as a " Paludina " (probably an Amnicola) which has 



' Attention has already been called to these facts by Dr. Stearns, but in or- 

 der to make the present discussion complete I have been obliged to restate 

 them briefly here. 



