116 University of Michigan 



reaction. However, with the operculum closed, they are unable 

 to attach themselves firmly to the branches and so are usually 

 shaken out in a few days by the wind. Nevertheless, specimens 

 often remain in hollows and crevices of the bark, although 

 their survival in such places appears to be comparatively rare. 

 Cerion uva appears more resistant to dessication, but the secre- 

 tive habits of Tudora enable it to withstand an equal amount 

 of aridity; the exposed cerions are dwarfed in the most arid 

 localities, but size in Tudora appears to have little or no 

 edaphic significance. 



In conclusion, the most remarkable case of parallel func- 

 tions, in different "cenoses" but in the same "mores" is 

 furnished by Cistulops raveni (Curacao and Aruba) and 

 Tudora maculata (Bonaire and Klein-Bonaire). These two 

 distantly related species are almost identical in habits and 

 must occupy practically the same position in their respective 

 societies. Although they differ in radula, operculum and 

 peristome, they resemble each other so closely in form, size, 

 color and sculpture, that, when I first found T. maculata, I 

 spent some time in a search for specimens with well-developed 

 apertures, under the impression that I was collecting im- 

 mature specimens of C. raveni or some closely related species ! 

 As already indicated, Thomas Bland probably neglected to 

 publish his "Cistula maculata" for the very same reason. 



Addenda 

 Since the preceding paper was finished. Dr. H. A. Pilsbry 

 has worked up the Pupillidae collected, and is publishing their 

 descriptions in the Proc. Acad. Nat. Sci. Philadelphia (1924). 

 As indicated below, he recognizes three species of Gastrocopta, 

 instead of G. longurio, and one species of Pupoides. 



Gastrocopta curacoana Pilsbrj^ 

 Widely distributed on Curasao (Cl-6, 11-15, 17), Aruba 

 (A2, 4, 5, 8), Bonaire (Bl-5, 8) and Klein-Bonaire (Kl). 

 Type locality: Fort Nassau, Curasao (C5d) ; new name for 

 Pupa longurio Cro.sse (1872), not Moquin-Tandon (1855). 



