1913.] NATURAL SCIENCES OF PHILADELPHIA. 669 



Nordenskiold ^ and Dall'' consider Gundlachia to be merely a dry 

 season or winter stage of Ancylus. As Dr. Dall expresses it, "an 

 Ancylus which has under favorable circumstances been able to form 

 a calcareous epiphragm and survive the winter, which ordinarily 

 kills the great mass of individuals, and while retaining the shell of 

 the first year, to secrete an enlarged and somewhat discrepant shell 

 during its second summer," this ability not being possessed by all 

 Ancyli. 



The rarity and sporadic occurrence of Gundlachia are apparently 

 favorable to this view; yet on closer inspection, less favorable than 

 at first appears. Of the Gundlachias I have myself collected, or 

 known from specimens taken in regions where the Ancylus fauna is 

 well known, not one can be regarded as a form of any known Ancylus 

 of the region. Each one of the known United States forms of 

 Gundlachia is specifically distinct from any Ancylus, wholly apart 

 from the septum-forming ability. The case would be quite different 

 if the only difference between a Gundlachia and some Ancylus of the 

 same fauna was the presence of a septum in some individuals. 



Ancylus commonly lives over winter in this latitude. I have 

 repeatedly collected specimens in the spring, in which the previous 

 season's growth was distinguishable from the new growth by greater 

 solidity and a coat of iron stain. In the Delaware River I have 

 taken specimens in winter from under stones at low water, in places 

 which had previously been covered with ice. In size they varied 

 from quite small to full grown. 



The only case known to me where a Gundlachia has been identified 

 with a known species of Ancylus is Nordenskiold's reference of a 

 form from the Chaco region to A. moricandi Orb. It is quite possible 

 that this identification might l^e altered on thorough comparison 

 of authentic specimens. 



Dr. Dall has proposed a convenient terminology for the post- 

 embryonic stages in the life of Gundlachia, as follows: 

 I. Ancyloid stage, shell simple, .4nc?/Zws-shaped. 

 II, Septate stage, a deck or septum added. 



III. Gundlachia stage,^ an Ancylus-like shell added to the margins 

 of the aperture of the septate stage, the latter lying obliquely upon it. 



The form in which there is no septate stage, and which is indis- 



3 Zoologischer Anzeiger, XXVI, 1903, p. 590. 



^ Nautilus, XVII, Jan., 1904, p. 97; American Naturalist, XLV, March, 1911, 

 p. 175. 



' The genus Gundlachia was originally described from specimens in the 

 "septate stage," but later was found in the third stage. 



