NOTES ON GUXDLACUIA AND ANCYLUS 



DR. WILLIAM HEALEY DALL 

 U. S. National Museum 



Ahoi-t seven years ago, 1 in the Nautilus I called at- 

 tention to certain problems connected with the genera 

 mentioned in the title of this paper, and urged investiga- 

 tion of the subject from the hypothetical view of the two 

 following propositions : 



1. That Gundlachia is merely an Ancylus which under 

 favorable circumstances has been able to form a cal- 

 careous epiphragm and survive the winter, which ordi- 

 narily kills the great mass of individuals, and, while 

 retaining the shell of the first season, to secrete an en- 

 larged and somewhat discrepant continuation of it dur- 

 ing the second summer. 



2. That not all Ancyli necessarily have the ability to 

 do this, but the practise may have developed in certain 

 small species; and in tropical regions where the dry 

 season takes the place of winter it is possible that sur- 

 vival may become more or less habitual with some of 



In this connection attention may be recalled to the 

 estivation in dry mud behind a double epiphragm, in the 

 Bahamas, of Segmentina dentata Gould, 2 and to the ob- 

 servations of Erland Nordenskjold 3 on Ancylus mori- 

 candi Orbigny, in Brazil. 



During the past four years I have received an inter- 

 esting series of notes by Mr. John A. Allen, of Cleve- 

 land, Ohio, connected with the Nungesser Electric Works 

 of that city, who has for some time been domesticating 

 in small aquaria species of fresh-water shells, including 



1 Nautilus, XVII, No. 9, pp. 97-98, January, 1904. 



'Smithsonian Misooll. Coll., Vol. 47, Pt. 4, No. 1566, pp. 446-448, 

 April, 1905. 



*Zool. Anzeiger, XXVI, pp. 590-593, July, 1903. 



