PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 589 



early in the development of the individual. The narrow columella is 

 similar in the two species. 



The specimens from Fray Bentos and Paysandu (where only a few were 

 taken), have no second angle below the upper spiral ridge on the back. 

 It is a very abundant snail at San Gabriel's Island. Specimens preserved 

 in alcohol become brown when dried ; and this is also true of most, prob- 

 ably all, of the dark green species. 



The figures by von Iterson, on Plate XXXIX, represent a very dark 

 green specimen. They are not so characteristic as that on Plate XLla, 

 which shows the back of an example with the color-pattern fully developed. 



POTAMOLITHUS PARANENSIS Sp. nOV. 

 (Plate XLI, Figs. 10, 11.) 



The shell is globose, with conic spire, olive-yellowish, smooth except for 

 fine growth-lines and very fine, indistinct spiral striae. Whorls strongly 

 convex, the last swollen below the suture, in its latter part flattened below 

 the swelling, rounded at the periphery and base. The aperture is very 

 oblique, ovate, outer lip thin and sharp. Columella moderately calloused. 



Fig. 11. Alt. 3.3, diam. 3 mm.; 3 whorls remaining, the apex eroded. 

 " 10. " 2.4, " 2.3 " 4 whorls, the apex perfect. 



Rio Parana at Puerto Bertoni, Paraguay, collected byA.de W. Bertoni, 

 No. 103,049, A. N. S. Phila., from No. 189, coll. Museu Paulista. 



From the sharpness of the outer lip, I am disposed to think that none 

 of the specimens is fully mature, though the largest one must be nearly 

 so, as it is eroded like an old shell. It differs from P. lapidum by the 

 longer spire, small size and pale color. There are two specimens in the 

 collection of the Academy of Natural Sciences of Philadelphia, three in 

 that of the Museu Paulista. 



POTAMOLITHUS DOERINGI sp. nov. 



The shell is subglobular with a short conic spire, solid and strong, 

 olive-colored, more or less streaked or mottled with black. The surface 

 is dull, lightly marked with fine lines of growth and extremely weak, 

 coarse spirals ; 3^ whorls of the spire remain, the apex being eroded in 

 adult shells. The whorls are strongly convex, parted by a deep suture, 

 which descends briefly at the aperture. The last whorl is convex through- 



