184 POPULAR CONCHOLOGY. 



having two triangular tentacula, with eyes at 

 the base; foot oval and thin. — 20 species re- 

 cent, 12 fossil. 



This genus is often united with the last, as 

 they are similar in most respects, differing 

 chiefly in the direction of their 

 spires ; (the Physce being generally 

 sinistral, and the Lymnece dextral 

 shells;) and also in the oblique plait 

 on the columella. They are abun- 

 dantly found in our rivers and ponds 

 (particularly the latter, as they appear to prefer 

 stagnant water), and in other parts of Europe, 

 Africa, and America : one or two species have 

 been mentioned as natives of India. They feed 

 on aquatic plants, and come to the surface of 

 the water for air, like the preceding genera ; 

 the number of their eggs is very great, and they 

 are deposited on stones, stems of vegetables, 

 &c. in long masses enveloped in a glairy sub- 

 stance. Darwin mentions finding Lymnece in 

 great numbers in a lake near Rio de Janeiro, 

 into which the inhabitants assured him the sea 

 annually, and sometimes oftener, entered, and 

 made the water quite salt. 



