530 patagonian expeditions: zoology. 



Section Undetermined. 

 Lymn^a andeana sp. nov. 



(Plate XLVla, Figs. 4, 4^.) 



The shell is acuminate-oblong, imperforate, very thin and fragile, pale 

 yellowish-corneous, translucent. Surface dull, smooth to the eye except 

 on the last part of the last whorl, where it is conspicuously malleated. 

 Under the microscope the dullness is seen to be caused by extremely fine 

 hair-lines, mainly longitudinal in direction, but forming a close mesh over 

 the whole surface. There are also faint growth-lines and weak traces of 

 spiral bands of vertical wrinkles. Whorls barely 4, the first convex, those 

 following only weakly so. The last whorl has the form of a long ellipse. 

 Aperture ovate. Parietal film scarcely perceptible. Columella slender, 

 slightly concave, dilated above, the dilatation thin and adnate. 



Length 11.9, diam. 6.3 mm.; aperture 7.3 mm. long. 



Near the base of the Andes in drying pools on a high divide, 50 miles 

 north of the Rio Chico. 



This species is apparently related to L. peregrina Clessin of southern 

 Brazil and Uruguay, but differs conspicuously by the very weak develop- 

 ment of spiral sculpture, that species being even more copiously striate 

 spirally than the North American L. columella. 



A few immature specimens of another thin, fragile species, probably 

 related to L. andeana, were taken in small streams on the Rio Chico, 10 

 and 25 miles above the Sierra Oveja. 



Planorbis peregrinus d'Orbigny. 



Planorbis peregrinus d'Orb., Voy. dans I'Amer. M^rid., p. 348. 



Rio Negro, Bahia Blanca, etc. (d'Orbigny); lakes along the Rio Negro 

 (Roca Exped.). 



Planorbis anatinus d'Orbigny. 



Planorbis anatinus d'Orb., t. c, p. 351 (Parana river, Prov. Entrerios, 

 Argentina). 

 Lakes along the Rio Negro (Roca Exped.). 



Family ANCYLID^. 



Ancylus concentricus bonariensis Strobel. 



A. c. var. bonariensis Strobel, Materiali, etc., p. 51, pi. 2, f. 4 (around 

 Buenos Aires). 



