BARBADOS-ANTIGUA EXPEDITION 203 
a land where a guaranty may be had that it will not be found. 
Two or three little Opeas, a small Helicina, a Succinea, and a 
Thysanophora—all sparingly found, about completes our list. 
Nearly all the little ponds and rivulets,—for the most part 
dry when we were in the island, contain several species of pul- 
monates. We took three species of Planorbis,—one of them the 
flat disk-like P. cultratus Orb., a Physa and some large Ancylus. 
Besides these we took one specimen of Pisidiwm. 
With the very great development of fresh-water mollusks in 
the United States and in Central and South America, it seems 
not a little curious that the Antilles possess no more than a few 
widely distributed forms. One would hardly expect the smaller 
islands to show much wealth of species, where the water courses 
are so small and uneertain, but the larger islands of the 
northern series with rivers and ponds that are never dry are 
almost destitute of fresh-water shells beyond a few species that 
seem to maintain themselves with difficulty. At all events, they 
have never developed any peculiar genera or species that are 
very characteristic of an Antillean fauna. The direct contrary 
is true of the land mollusks. 
