H22 Bulletin American Museum of Natural History [Vol. LIII 
C.; Italy); Ostrea cucullata Born (45° C.; New Britain); Bythinella 
peraudiert Bourguignat (42° C.; Algeria); Lymnzxa peregra Miiller 
(29° to 46° .25 C.; Pyrenees, Iceland, Italy); Lymnza truncatula Miller 
(32° to 42° .5 C.; Iceland, Italy); Physa heterostropha Say (41° C.; 
Virginia); Paludestrina nickliniana (Lea) (41° C.; Virginia); Melanopszs 
etrusca Villa (41° C.; Italy); Pistdium casertanum (Poli) var. thermale 
Dupuy (39° C.; Pyrenees); Paludestrina protea (Gould) (88° C.; south- 
ern California); Fluminicola merriami Pilsbry and Beecher (86° C.; 
Nevada); Tryonza clathrata Stimpson (86° C.; Nevada); Physa acuta 
Draparnaud (38° to 35° C.; Pyrenees); Planorbis corneus (Linneus) 
(34° C.; Italy); Melanoides tuberculata (O. F. Miller) (82° C.; Algeria) ; 
Melanopsis jordanica Roth, M. premorsa (Linneus), and Neritina sp. 
(82° C.; Palestine); Theodoxus fluviatilis (Linneeus) (82° C.; Italy); ete. 
A few of these, such as Bythinella thermarum and Melanopsis etrusca, 
appear to be restricted to thermal springs. Most of them, however, are 
forms of species found elsewhere at a normal temperature. Thermal 
waters are usually very poor in oxygen, especially when they issue from 
boiling springs. On the other hand, they often show a concentration of 
salts dissolved (carbonate of lime, silica, sodium salts, arsenical com- 
pounds, etc.) much above the normal. As a rule, both of these factors 
influence the nature of their fauna much more than the increased 
temperature. 
There are a number of hot springs in the Belgian Congo, notably in 
Katanga,' and it would be of great interest to know whether any of the 
local aquatic snails have become adapted to them. Those which the 
junior author visited contained no mollusks. Volcanic eruptions may 
sometimes temporarily raise the temperature of the water so as to kill 
off all life. This happens periodically in the northern part of Lake Kivu, 
where lava-flows have been known to bring the water near boiling point, 
causing the death of quantities of fish. This peculiar condition may be in 
part responsible for the exceedingly scant molluscan fauna of that lake. 
In those parts of the Belgian Congo where the alternating wet and 
dry seasons are very pronounced, the aquatic mollusks, with the excep- 
tion of those that inhabit permanent rivers and larger lakes, must be 
able to stand the severe drought. When the rains are at their height 
inundations are liable to flood extensive level areas and the floods then 
carry many aquatic snails far away from their permanent haunts. Inthe 
succeeding dry season the waters gradually retreat and extreme arid 
‘Matthieu, F. F. 1913. ‘Les sources thermales du Bas-Katanga.’ Ann. Soc. Géol. Beloi : 
Publ Halas Oboes Ole Ie le ce r a eave 
