590 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



out. Aperture quite oblique, large, white within. Peristome black, a 

 little contracted, more so above, black. Columella and parietal wall 



'g- 'i 7-) 



4- 



FIG. 17. Potamolithus doeringi. 



moderately calloused, the edge black, continuous. There is a concave, 

 crescent-shaped umbilical area defined by an angular ridge. 



Length 7, diam. 7 mm.; length of aperture with peristome 5.7 mm. 



Salto do Yguassu, Province of Missiones, Argentina, collected by Dr. 

 H. von Ihering, June, 1910. 



This is a larger species "than P. lapidum (d'Orb.), with the last whorl 

 decidedly more dilated, the aperture more oblique, and a crescentic umbili- 

 cal area developed. When collected, the shells were heavily coated with 

 black ferrous material and most of them bear egg-capsules on the shell. 



POTAMOLITHUS PAYSANDUANUS von Ihering. 



(Plate XLIa, Figs, i, ia.) 



Potamolithus paysanduamis \. Ihering, Nautilus, XXIV, 1910, p. 15, with 



forms sinulabris and impressus. 



The shell is imperforate, solid, subglobular, olive-colored, smooth except 

 for weak growth-lines, shining. The spire is very low, conic, the apical 

 whorls eroded in all the individuals seen ; three whorls remaining are 

 strongly convex. The last whorl is swollen below the suture, then some- 

 what flattened, rounded at the periphery and base. The suture descends 

 abruptly to the aperture in fully adult shells. The aperture is somewhat 

 oblique, ovate. The peristome is black, with obtuse, flat edge ; the outer 

 and basal margins are narrow ; the upper part of the outer lip and the 

 upper angle are wide, and the columellar and parietal margins are very 

 wide and flat, black, contracting the aperture. 



