PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 555 



mm. long. Some others in the same lot are smaller and more pupiform, 

 with the parietal callus barely free from the preceding whorl, as in fig. 8, 

 length 1.7 mm. The entire lot from the type locality consists of shells 

 which do not depart much from the normal Littoridina contour. 



At two stations, 40 and 50 miles above the Sierra Oveja, a considerable 

 proportion of the shells have the last whorl deeply descending to the aper- 

 ture and becoming free, or partially free near the termination. A series 

 from 40 miles above Sierra Oveja is figured, PI. XLII, figs, n, na, 12, 

 13. Fig. 12 represents a nearly normal shell; figs, n, na and 13, 

 those with the last whorl loosening its coil ; all are fully mature, but not 

 old snails. The individuals figured measure : 



Fig. ii. Length 3.3, diam. 1.7, length of aperture 1.2 mm.; whorls 

 " 12. " 2.7 " 1.6 " 1.25 " " 



" 13. " 2.1 " 1.3 " " i " " 



The same tendency is well-marked in a lot from far down the river, 

 below the mouth of the Rio Chalia. The other lots of the species resemble 

 the type lot, having the shape nearly normal, but with a variable proportion 

 of individuals in which the peristome is partly or for a short distance free. 



L. hatchen is thus a species distinctly aged or gerontic, with this feature 

 much more strongly emphasized in certain colonies. 



LITTORIDINA SIMPLEX sp. nov. 



(Plate XLII, Figs. 9, 10.) 



The shell is minutely rimate but scarcely perforate, rather thin, ovate- 

 conic, of a very pale olivaceous-yellowish tint, the apex and first whorl 

 reddish in the type lot, smoothish, but lightly marked with growth-lines. 

 The spire is straightly conic, the apex minute and very slightly obtuse. 

 Whorls 4^ , all rather strongly convex, regularly enlarging, and joined 

 by an impressed suture, which on the last whorl or two shows a narrow 

 faint margination below caused by transparence. The aperture is ovate, 

 subvertical. Peristome continuous, its edge delicately marked with a 

 brownish line. The outer lip curves forward a little in the middle, and 

 has a very delicate whitish thickening within. Inner margin thickened a 

 little, continuous, in contact with the preceding whorl. 



Fig. 9. Length 3, diam. 1.8 mm., length of aperture 1.3 mm. 

 I0 3 2 : 5 



