PILSBRY: NON-MARINE MOLLUSCA OF PATAGONLA. 579 



and conic, the apex obtuse. Whorls 4, convex, the last evenly rounded, 

 without keels or angles, the suture shortly deflexed at the aperture. There 

 is a moderate or narrow and usually rather conspicuous columellar area. 

 The aperture is oblique, rather broadly ovate. The peristome is thick- 

 ened within, the basal and outer margins are evenly and strongly arcuate, 

 the outer becoming straightened near the upper angle of the aperture. 

 The inner lip is heavily calloused ; columella rather wide and flattened. 



Length 3, diam. 2.8 mm. 



Rio de La Plata, at San Gabriel's Island, near Colonia, province of 

 Colonia, Uruguay. Types, 69,683, A. N. S. P. 



Development.- -The young of about three whorls and 2 mm. diameter 

 are essentially similar to the adult stage in shape. The columella is 

 somewhat wider in proportion. 



This is the smallest Potamolitkus now known. It has the globular shape 

 of P. lapidum, but the wide columella of the neanic stage shows that P. 

 agapetus is related to P. buschii. It differs from P. buschii by the evenly 

 rounded shape of the last whorl, the diminutive size and clear green color, 

 as well as by the total absence of a peripheral angle or keel ; but the 

 young stages of P. buschii are not always readily distinguishable from im- 

 mature P. agapetus. 



In some shells the aperture is smaller than in that figured, by reason 

 of a greater descent of the last whorl immediately behind the lip. The 

 columellar crescent varies from quite narrow, almost linear, to quite wide 

 and concave. 



POTAMOLITHUS CHLORIS Sp. nOV. 

 (Plate XLU, Figs. 8, 8.) 



The shell is imperforate, rather solid, ovate conic, light green, the spire 

 paler, summit corneous. The spire is straightly conic, apex minute, 

 slightly obtuse. Whorls 4^ , convex, the last evenly rounded through- 

 out, expanding near the aperture. The aperture is very oblique, shortly 

 oval. The peristome is slightly expanded, obtuse. Columella and 

 parietal wall heavily calloused, the former flattened, rather wide. 



Length 3, diam. 2.5 mm., length of aperture 1.8 mm. 



Salto das Cruzes, Rio Tiete, State of Sao Paulo, Brazil. Type, No. 

 103,046, A. N. S. P. from No. 106 Museu Paulista. Collected by Hase- 

 mann, 1908. 



