PILSBRY: non-marine MOLLUSCA of PATAGONIA. 583 



Length 5, diam. 4.8 mm. 

 " 4-5 " 4-5 " 



Uruguay River, at Paysandu, Uruguay. Types, No. 69,696, A. N. S. P. 



In the typical form of the species the flattening of the last whorl is 

 nearly vertical below the shoulder. In other examples (PI. XL, figs. 2, 3) 

 the flattened surface slopes steeply, and the periphery is somewhat more 

 angular, though still rounded off. Young shells (PI. XL, figs. 4, 4a) with 

 S}i whorls, having a diameter of 2.5 mm., have a distinct flattening above 

 the periphery, though less marked than in adults. This was not seen by 

 my artist, who drew the peripheral region of fig. 4 much too regularly 

 rounded. Fig. 5 represents a slightly larger shell, diam. 2.8 mm., the 

 basal aspect drawn to show the very broad, flat, columellar callus. In 

 contour it resembles fig. 2. 



P. oybigiiyi is somewhat related to P. dinochilus, but differs in the 

 lower varix, absence of a spiral ridge below the suture, the larger columellar 

 area, broader columella, etc. It is similar to P. pJiilippiauiis in shape, 

 but lacks the columellar furrow of that species. 



POTAMOLITHUS JACUHYENSIS Pilsbry. 

 (Plate XXXIX, Figs. 3, ^a) 



Potamolitlms jaciihyensis Pilsbry, Nautilus, XII, p. 113, Feb., 1899. 



The shell is globose, solid and strong, smoothish, with the usual slight 

 growth lines and scarcely visible spirals ; covered with a strong, rich brown 

 cuticle, becoming more reddish towards the apex, and dark green below 

 the last turn of the suture, behind the lip, and at the base. Spire short 

 and conic. Whorls 43^ , those of the spire convex, the last very obtusely 

 biangular, being flattened peripherally, subangular at the shoulder, flat- 

 tened and sloping above it, and tapering basally. There is in some 

 specimens a well-developed flattened columellar crescent, but in other 

 individuals it is reduced and inconspicuous. The aperture is large and 

 somewhat spreading, moderately oblique and irregularly semicircular. 

 The outer lip is sharp, with a dark line at the edge, not expanded, and 

 not in the slightest degree varicose or contracted. The inner lip is 

 heavily calloused. 



Length 6, diam. 5.6 mm. 



Jacuhy River, Rio Grande do Sul, Brazil. Types, 61,820, A. N. S. P., 

 collected by Dr. H. von Ihering. 



