040 Bulletin American Museum of Natural History [Vol. LIII 
which I éan see the muskrat could obtain the body of one of these larger 
mollusks is by leaving the animal out of the water until it becomes weak 
or until it dies, when the valves could be easily separated.’”’ A. G. Apgar 
found that when the Unzo is traveling along, its foot projects a half inch 
or more from the lower side of the shell. If, while the foot is in this, its 
usual, condition, the two valves be pinched, the foot will be caught 
between the closing shell; if the pinching be continued for a half or three- 
quarters of a minute, the animal, probably from the pain produced, be- 
comes paralyzed and unable to make use of the adductor muscles. Now, 
if the shell is released, it will fly open about one-half inch, and can easily 
be torn entirely open. The strength needed to keep the foot from being 
drawn into the shell is not great, being far less than that of the jaws of 
the muskrat.!. The procedure has, it would seem, not been observed 
with the muskrat itself. It is of some interest that shortly after its recent 
introduction into Bohemia (1906) this animal has taken to feed partly 
upon European unionids.? 
In Europe rats and otters destroy large quantities of fluviatile mol- 
lusks and they have been known to break through the ice in order 
to reach this prey. We ‘know of nomammal in Africa, excepting 
perhaps the otters, that selects fluviatile mollusks as food. They are, 
however, relished by the natives of many tribes, especially Etheria, 
Egerva, and certain large Mutelide (Aspathariawissmanni, A.sinuata,ete.). 
In densely settled parts of Europe and North America sewage from 
the cities and waste products of certain industries emptied in large 
quantities in the rivers, have practically wiped out aquatic molluscan 
life in many districts. On the other hand, the pearly Unionide are fished 
for the manufacture of buttons and this industry has grown so much 
within the last thirty years in the valley of the Mississippi that several 
of the more valuable species are nearing extinction.‘ 
Mollusk Fauna of Stagnant Water 
Open, shallow pools of small size are in the Belgian Congo the pre- 
ferred habitat of Lymnza natalensis undussumz, Physopsis africana, and 
certain species of Planorbis. These snails are found in the savanna 
‘Apgar, A.C. 1887. ‘The muskrat and the Unio.’ Journ. Trenton Nat. Hist. Soc., No. 2, pp. 58— 
59. 
pols Strassen, O. z. 1914. ‘Brehms Tierleben.’ 4th Ed. Saugetiere, II, (Leipzig and Vienna), 
0: ; 
oa ’Lawson, A. K. 1921. ‘Limnza stagnalis destroyed by rats.’ Journ. of Conchology, XVI, 5, p. 
“43mith, H. M. 1899. ‘The mussel fishery and pearl-button industry of the Mississippi River.” 
Bull..U. 8. Fish Comm., XVIII, (1898), pp. 289-314, Pls. yxv—Lxxxv. ih ‘ 
ome researches are at present (1923-1924) being carried on in the Belgian Congo in order to find a 
new supply of pearl-button mussels, but from what we know of the unionid fauna of that district they 
~ are not likely to prove very productive. 
