600 Bulletin American Museum of Natural History . [Vol. LIII 
Saulea, and Afropomus, have corneous opercula, like the tropical 
American genera. This family is not represented, recent or fossil, in 
north temperate regions. 
The Melaniide or melanians of Africa are partly velnied to those of 
the Oriental Region (Melaniide), but the genus Potadoma (Potadomine) 
is closely related to the Tropical American genus Pachychilus. Rhino- 
melania was considered by E. von Martens to be a subgenus of the South 
American genus Hemisinus. It does not appear related to any Old 
World genus. 
All of the fresh-water forms mentioned are large or moderately large 
shells, generally occurring in abundance. Their absence in Europe and 
especially in western North America, though negative evidence, has a 
certain significance. From the Laramie formation (Upper Cretaceous) 
on, rich faune of Unionide, Cyrenids, Viviparide, Melaniide and 
other fresh-water mollusks are known in western North America. If the 
Ampullariide, Mutelide, Etheriide, etc., migrated to or from South 
America around the North Pacific, it is certainly strange that no trace of 
them has been found in these deposits. 
The absence of these African and South American families in Euro- 
pean Mesozoic and Tertiary faunz yet known renders migration around 
the North Atlantic unlikely. 
Some other groups common to the fresh-waters of Shih America 
and Africa, such as Cyrenide, Hupera, Neritina, Amnicolide, are well 
represented in northern Mesozoic and Tertiary deposits. Thus, the 
genus Hupera is now confined to the Ethiopian Region, South and Middle 
- America. It would be thought an evidence of former union of these 
continents, were it not that species have been found in the Eocene of 
Europe, China, and western North America, showing that it is a group | 
formerly having a Holarctic range, probably migrating south and now, 
like the camels, existing in the peripheral areas of its migrations. 
TERRESTRIAL Moutusks.—Among land mollusks the Acavide, 
Streptaxide: and Achatinide are the most significant families. The sub- 
family Streptaxine is special to Africa and South America. The sub- 
family Ptychotremine is distributed over Africa and the Oriental 
Region. Two Italian Eocene species and one French Pliocene species 
have been referred to the group, but their relations have been disputed 
and must be regarded as uncertain. Otherwise the family is unknown in 
northern regions. 
The Achatinide have their greatest development in Africa, but with 
numerous genera also in tropical America and a few in the Oriental 
Region, all of the latter identical with or close to African genera. 
