PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 591 



Length 4.8, diam. 3.9 mm. 



Paysandu, Uruguay. Dr. Florentine Filippone. Types, No. 103,070, 

 A. N. S. P. 



This form differs from P. lapidum by its contracted aperture, the inner 

 and upper margins of the peristome being heavily thickened within, the 

 thickening covered with a blackish cuticle. In P. lapidum the aperture 

 is ample, with no such heavy thickening. In the stage immediately pre- 

 ceding maturity the columella has a moderate white callus within, and 

 the parietal callus is quite thin. The type specimen is figured. Six 

 others I have seen show no significant variation. 



With these specimens two other forms were sent which seem to be 

 phases or varieties of the same species, but not intergrading in the mate- 

 rial examined. Whether they occurred in the same or in separate colonies 

 is not known. 



Form SINULABRIS (Plate XLIa, figs. 2, 3). The shell differs from typical 

 P. paysanduanus by having a low rounded ridge behind the outer lip, 

 which is black, contracted, and has a rounded sinus above. The basal lip 

 is narrow and a little retracted. The columellar and parietal margins are 

 not so broad as in paysanduanus. There is an excavated umbilical area, 

 but it is generally not distinctly defined by an angle. The shape is other- 

 wise as in P. paysanduanus. 



Length 4.5, diam. 4.9 mm. 

 "4 "4 " 



Form IMPRESSUS (PI. XLI#, figs. 4, 40). The shell resembles typical 

 paysanduanus as far as the middle of the last whorl, after which it has an 

 impressed, concave zone a short distance below the suture, and usually a 

 sinus in the upper part of the lip. The outer lip is thin and sharp, with 

 no external varix or swelling. The shell, under the cuticle, is light yellow. 



Length 5, diam. 4.8 mm. 



Up to the time of reaching the size of adult P. paysanduanus, this form 

 grows normally. After that, instead of forming a contracted aperture, it 

 adds a half whorl, which is distorted by a superior concave zone and finally 

 terminates with a thin outer lip. The specimens were sent with typical 

 paysanduanus. 



