PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 551 



but slightly convex, rarely carinate ; aperture ovate, not very oblique, less 

 than half as long as the shell ; peristome thin and simple, continuous or 

 interrupted. The operculum is thin, ovate, paucispiral, the nucleus below 

 the lower third and near the columellar margin. The long penis has 

 several digitate lateral papillae or simple warts, and is curved at the end. 

 The central tooth of the radula has one to four basal denticles on each 

 side. The marginal teeth have very numerous denticles, more than twice 

 as many as the admedian tooth. The animal is oviparous. 



DENTITION OF LITTORIDINA. 



Littoridina guadichaudii, the type of the genus, has several, probably 

 four, basal denticles on each side of the central tooth. Souleyet's figure 

 shows five, but allowance must be made for the difficulty of the object and 

 the date, 1852. 



Dr. von Ihering found two basal denticles on each side in L. australis. 

 For L. picium he gives the number ^ and L. charruatia ^. 



L. simplex of the Rio Chico (fig. 8) has a central tooth with the cusp- 



FIG. 8. 



Central tooth of Littoridina simplex Pils. 



formula ^. The admedian tooth has 6, i, 6 cusps, the two marginal 

 teeth many, about 30, cusps. 



L. hatcheri, Rio Chico, has the cusp formula ^. 8. 25. 30. The cusps 

 of the marginal teeth are so excessively small that their exact number is 



not certain (fig. 9). 



FIG. 9. 



Teeth of Littoridina liatcheri Pils. 



Littoridina was based upon a snail from the river of Guayaquil, having 



