PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 



523 



tonica. It is possible that the presence of acid in the water, causing erosion 

 of the shell, may also account for the stunted stature of these forms. 



DENTITION OF SOUTH AMERICAN LYMN^EAS. 



Dentition of L. viator d'Orb. The radula examined was from one of 

 the specimens taken on the Rio Chico near the Sierra Oveja. The central 

 tooth is narrow and unicuspid as usual. There are three or four lateral 

 teeth, having two long cusps. In the following transition teeth the inner 

 cusp (entocone + mesocone) is long and bifid, ectocone simple. The 



FIG. i. 



Teeth of Lymneea viator d'Orb. Rio Chico, Patagonia. 



marginal teeth are very oblique, with three cusps, entocone, mesocone and 

 ectocone. In some of the outer marginal teeth there may be one or two 

 minute accessory cusps. 



The radula of L. viator agrees well with that of the European L. trun- 

 catula as figured by Lehmann. It differs from typical Lymncea by retain- 

 ing the primitive tricuspid type of teeth in the marginal series, with few 

 small accessory cusps or none. Lymnaeas with this type of teeth have a 

 continuous distribution from Patagonia to Alaska and in the Palaearctic 

 region. 



Dentition of Lymncea diaphana King. These are about 30, 7, I, 7, 

 30 teeth. The central tooth is wider than usual in Lymneea, unicuspid. 

 The lateral teeth are bicuspid, the broad inner cusp becoming bifid on 

 the transition teeth. The inner marginals have the mesocone and ento- 



FlG. 2. 



^ -^Mtf*\jiBtf 



Teeth of Lymtuza diapfianalfcaig. Rio Chico, Patagonia. 



cone split into four to six small cusps, the ectocone remaining simple. 

 Further out the marginals become transversely lengthened, their cusps lie 



