282 HAAS: ABIDA AND CHONDRESTA. 



which have the outer and inner margins of the peristome 

 united by a strong callus, forming a continuous peristome, 

 which may even stand free of the last whorl. 



Such specimens with continuous peristome, as also those 

 without the connection, either as a mark of age or in conse- 

 quence of life in a locality rich in lime, can thicken the peri- 

 stome and form tooth-like foldlets on the inner and outer 

 margins, interposed between the usual folds of the affinis type. 

 If this structure of peristomal folds extends upon the upper 

 margin also, we have Bourguignat's Pupa andorrensis. 



The transition-stages to the complicated andorrensis are 

 illustrated in pi. 25, figs. 10, 11, by two specimens from the 

 Congost de Organya in the Segre Valley. 



A correct systematic disposition of andorrensis has been 

 difficult on account of the peculiar structure of the basal keel 

 and the conformation of apertural folds as inferred from 

 Bourguignat's original figures, since the form has not hitherto 

 been represented in other collections. Bourguignat himself 

 mentioned for comparison P. polyodon (Drap.), apparently 

 led astray by the purely superficial similarity of the system 

 of peristomal folds. Bofill and I, by the aid of our extensive 

 material, were the first to recognize andorrensis as a local 

 race of A. affinis. It is moreover to be intimated that none 

 of the many specimens examined by us attains to the 

 strength of the peristomal folds of Bourguignat's original 

 figure. However, as I have had opportunity to compare 

 Bourguignat's types with the figures he gave, I know that 

 this investigator exaggerated in his figures the peculiarities 

 thought to be characteristic of the snails he was illustrating. 

 "With this procedure in mind, the difference between the orig- 

 inal figure and our material may be minimized. 



A. affinis andorrensis is moreover subject to great fluctua- 

 tion in length of the she'll. In the Congost of Oliana live 

 specimens of 10 mm. long, 3.75 mm. cliam., together with 

 others of 12 mm. long and 3 mm. diam. ; and one from Isobol 

 in the upper Segre valley measures only 8 mm. long, 3 mm. 

 diam. 



This local race is restricted to the valley of the Segre so far 



