PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 543 



arcuate, having a very small and low fold close to the upper end, and 

 hardly noticeable in most specimens. 



Length 5.1, diam. 3.8, length of aperture 4.3 mm. 



Springs on the Rio Chico, 25 miles below the Sierra Ventana, Feb. 15, 



1899- 



This species is known from 40 specimens in two lots, taken the same 

 day in the same neighborhood, but apparently from two springs, the sta- 

 tion numbers being different and the condition of the specimens as 

 regards erosion slightly diverse. There is also another individual from a 

 different station, "freshwater spring on the Rio Chico," date and locality 

 not given. They range in size from young shells less than 3 mm. long 

 to slightly over 5 mm. In a shell of 3 mm. there are fully three whorls. 

 All the adults have the spire worn, so that the number of whorls is un- 

 certain, but there are evidently four or more. 



The very globose shape of these shells shows that they are not young 

 or dwarf individuals of the larger species of the same region. Moreover, 

 the larger ones have the eroded and old appearance of adult snails. 

 Whether the species attains greater size in the streams running from the 

 springs which they inhabit remains uncertain. I know of several instances 

 of dwarf snails inhabiting springs, having put at least one such case on 

 record. 1 It is evident that the usual explanations of dwarfing in small 

 quantities of water are not pertinent, since in flowing springs there is no 

 lack of aeration and no accumulation of the toxines of metabolism. It 

 seems likely that the dwarfing of snails in springs may be due to the 

 purity of the water, which affords an insufficient supply of diatoms, other 

 algae and vegetable food. 



This form is, for the time being, ranked as a subspecies of Chilina monti- 

 cola from Punta Arenas, but I suspect that it is related rather to C. ftilgu- 

 rata. Apparently adult shells are only about half the size of monticola. 



CHILINA TEHUELCHA d'Orbigny. 



Cliilina tehuelcha d'Orb., Voy. dans 1'Amer. Merid., p. 336, pi. 43, figs. 6, 

 7 ; Strobel, Mat. Malac. Argent., p. 43, with var. mendozana, p. 43, 

 pi. 2, fig. 4. 

 A very obese, solid species with short spire and very large aperture. 



Length 35, diam. 25 mm. 



1 Cf. Goniobasis comcdensis fontinalis, Proc. A. N. S. Phila., 1906, p. 169. 



