14 THE NAUTILUS. 



NOTES ON GUNDLACHIA. I. 



BY BRYANT WALKER. 



The validity of the genus Gundlachia Pfr. is one of the disputed 

 points in systematic conchology. 



The article by Hedley, reprinted with notes by Dr. Pilsbry in the 

 NAUTILUS in 1895 (Vol. IX, p. 61), gives a very complete summary 

 of the data down to that date. The only omission in regard to the 

 North American forms that I have found, being the citation of G. 

 ancyliformis Pfr. from Palma Sola, Manatee Co., Fla., by Simpson 

 in 1888 (Con. Ex., II, p. 96). 



So far as I have been able to ascertain, no additional data in re- 

 gard to our species have been published. 



In the NAUTILUS for January, 1904, Dr. Dall called attention to 

 a very interesting account by Nordinskiold of a septa-forming An- 

 cylus from South America and expressed the opinion that the 

 so-called Gundlachise are merely Ancyli, which under favorable con- 

 ditions are able to protect themselves from drought and cold by 

 forming an epiphragm and subsequently ' to secrete an enlarged and 

 somewhat discrepant shell." 



The occurrence with typical Gundlachia of non-septate individ- 

 uals indistinguishable in shell characteristics from Ancylus has been 

 noted by several writers. Hedley, who believes the genus a valid 

 one by reason of anatomical differences, apparently inclines to the 

 view that "in unfavorable circumstances a septum is never formed." 

 While Dr. Pilsbry (NAUT., IV, p. 48), speaking of this apparent co- 

 existence of two forms, remarks, that if correct, " Gundlachia will 

 furnish the most extraordinary case of dimorphism known among 

 our American mollusks." 



During the last few years I have had occasion to examine criti- 

 cally large numbers of our Eastern American Ancyli, and until 

 within the last year, with the exception of a small series collected by 

 Ferriss near Joliet (to be discussed later), I have discovered no ten- 

 dency whatever to septa-forming in any instance. 



Recently, however, material from Ohio, Indiana, Alabama and 

 Mississippi has been received, which is of considerable interest as 

 bearing on the question, and the evidence thus afforded is herewith 

 submitted for consideration. 



