PILSBRY : NON-MARINE MOLLUSCA OF PATAGONIA. 529 



an entire specimen (fig. ii) there are ^/i convex and rapidly enlarging 

 whorls, the last inconspicuously marked with rather widely spaced, very 

 low longitudinal wrinkles, and some weak malleation in places. The 

 aperture appears to be less rounded than in L. patagouica. The parietal 

 and axial callus is a mere transparent film (not distinct as shown in fig. 

 1 1 ), closely adnate throughout. The columella is white, solid and rounded, 

 nearly straight, and without trace of a fold. The largest specimen (fig. 

 1 1) measures : 



Length 6.8, diam. 4.8, aperture 4.9x3.1 mm. 



Rio Chico, 25 miles below the confluence of the Rio Belgrano, in the 

 river under stones, numerous specimens. Also in a pool near the Sierra 

 Oveja, one characteristic individual. 



Most of the adult examples taken are very much eroded, the spire re- 

 moved, and the last whorl deeply eaten in places, as though by acid. 

 The parietal callus is thick, with the outer edge distinctly raised. The 

 external erosion is compensated by thickening of the shell from the inside. 

 Fig. 10 measures : 



Length 5, diam. 4, aperture 4.1 X 3 mm.; 25^ whorls. 



Although the perfect and the deeply eroded shells were in one lot when 

 received, yet I have no doubt that they came from two sources, one of pure 

 water, the other carrying CO2, doubtless from leaching through decaying 

 organic matter. 



Lymn^a pictonica Rochebrune et Mabille. 



Limncca pictonica R. et M., Miss. Sci. Cap Horn, p. 21, 1889. 



A small, very fragile species, with exserted spire and truncate apex, 2 or 

 3 convex, rapidly increasing whorls remaining. There is a very narrow 

 perforation. 



Length 6, diam. 3 mm. 



Picton Island, in the southeastern termination of the Beagle Channel. 



This species seems to be decidedly narrower than the preceding. It 

 may be the southern terminal member of the series of short Lymna^as 

 represented in the Magellan district by L. patagouica and on the Rio Chico, 

 400 to 500 miles farther north, by L. p. riochicoeiisis. It is quite possible, 

 however, that these several forms may prove to be independent shortened 

 forms, each directly related to more normal forms. 



