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THE AMERICAN NATURALIST [Vol. XLV 



Ancylus and Gundlachia. His observations extend over 

 some six years and his notes contain so much of interest 

 that it has seemed desirable to summarize and publish 

 his data, thus placing on record facts which may stimu- 

 late others to follow his example. 



Mr. Allen was kind enough to send to the museum a 

 lot of Anacharis supposed to contain both Ancylus and 

 Gundlachia in the living state, and numerous specimens 

 of the former were observed in a jar to which the vege- 

 tation was consigned, immediately after it was filled 

 with water. We were not able to distinguish with cer- 

 tainty any Gundlachia, though some may have been pres- 

 ent, and the small aquarium was kept in good condition 

 to await developments. This was in December, 1907. 

 The Ancyli continued to exist in apparent health during 

 the winter. In May, 1908, they seemed to go into hiding, 

 but during the summer reappeared again in rather dimin- 

 ished numbers, while a few young ones were observed. 

 No particular change was noticed during the following 

 winter and spring. While absent during the summer of 

 1909, it became necessary to transfer the collections to 

 the new building of the National Museum and the aquaria 

 were set aside. After the confusion of the transfer was 

 measurably over, I examined the aquaria and, finding 

 nothing visible, had the contents of the smaller one 

 (about 8 X 4 X 10 inches in size) removed and submitted 

 to the most careful scrutiny, the sand at the bottom 

 being placed in a fine sieve for examination, but not a 

 trace of Ancylus remained. I concluded that there had 

 been sufficient carbonic acid in the water to completely 

 dissolve these fragile shells after death, and that some 

 unfavorable condition had exterminated the colony. In 

 the other aquarium, which was about eight times the ca- 

 pacity of the smaller one, the water had evaporated to 

 about half its normal quantity and no mollusks except 

 a few small LymnaBas were visible, while the Anacharis 

 had suffered considerably by the adverse conditions. 

 This was towards the end of November, when it was 



