PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 595 



very concave, and not wider than the outer lip, and is bounded outside by 

 a linear, hardly noticeable columellar area. 



Length 5.5, diam. 4.9 mm. 



Uruguay River, at Paysandu, Uruguay. Type, No. 90,218, A. N. S. P. 



This species is based upon a single specimen, quite adult and to all 

 appearance perfectly normal, yet so unlike other known species that its rela- 

 tionships are doubtful. The prominent characters of P. hatcheri are the 

 elevated and tapering spire and the approximation of the two angles of the 

 last whorl, the upper one finally dominating, while the lower becomes obso- 

 lete on the last half of the last whorl. The absence of a lip-varix and of 

 a noticeable columellar area, as well as the rather narrow columella, are 

 features like the P. lapiditm group. The young shell, up to the middle of 

 the penultimate whorl, must be ovate, without angles ; but in the absence of 

 immature specimens, not much can be said of the development of the species. 



It is named to honor Mr. J. B. Hatcher. 



POTAMOLITHUS DINOCHILUS Pilsbry. 

 (Plate XXXVIII, Figs. 5, 7, 7 a, 76, 8.) 



Potamolithiis dinocJiiliis Pilsbry, Nautilus, X, p. 87, Dec., 1896. 



The shell is globosely trochoidal, imperforate, very solid and thick ; 

 green, profusely marked with irregular, zigzag buff streaks. The surface 

 is smoothish, with the usual faint growth-lines and indistinct fine spiral 

 striae. The spire is conic, rather high when preserved entire (fig. 8), but 

 worn to a blunt summit in all adult shells seen. There are 4^ whorls, 

 but only 2^ to 3 remain in adults. The earlier whorls are rounded, but 

 at the beginning of the last a small ridge arises a short distance below the 

 suture. The last whorl is somewhat flattened and slopes steeply to the 

 basal periphery, which is full and narrowly rounded or subangular. The 

 ridge below the suture is narrow, but well developed on the back. The 

 columellar area is ill-defined and very narrow. The lip is strengthened 

 by a varix, which above the periphery is very high, massive and recurved, 

 but becomes weak at the base. The aperture is very oblique, contracted, 

 irregularly rounded, with the margins built out beyond the varix, con- 

 tinuous around the mouth, thick and obtuse. The columella is strongly 

 concave, and moderately calloused, not more than the lip generally. 



Length 4.9, diam. 5.2 mm. 

 " 4-5 " 5 " 



