28 



LAND AND FRESII-AVATER SHELLS OF N. A. [PART IL 



Fig. 31. -wholly by its white color, and hardly by a perceptible 



elevation, leaving scarcely any trace of an umbilicus. 



Animal ? 



Habitat. — In the fresh-water lakes of North America. 



I compared twenty specimens from Lake Erie which 

 appeared perfectly adult and whose characters were 

 constant. This species certainly much resembles L. 

 stagnalis ; but the invariable tawny color, the decided 

 almost regular striation, the narrower aperture, the 

 outer lip less curved and not prominent, and, finally, the 

 delicate, closely adherent, white colnmellar callus suffi- 

 ciently distinguish it. {Rossmassler,^ 



Limnceusspeciomf,. Moquin-Tantloii (Moll. Fr. II, 471) places L. 

 appres&a, Say, in the synonymy of L. stagnalis, 

 var. C, roseolabiota (L. hicnJor, Mke, L. stagnalis, var. obscurvs, 

 Mke.). 



Reeve (Brit. L. and Fr. W. Sh.) does not quote Say's species 

 in the synonymy of L. stagnalis, but on p. 1.55 notices the marked 

 degree of parallelism between, if not identity of, L. limosa and 

 L. catascopium, L. auricularia and L. macruystoma,^ L. stagna- 

 lis and L.jugularis, L. jMlustris and L. elodes, and L. truncatula 

 and L. desidiosa. 



Limneea stagiiflis is catalogued l)y Middendorf among the 

 circumpolar species of Asia. It is found in Europe, Siberia, and 

 Cashmere. Like many of our extreme northern species, it appears 

 common to the three continents. 



Fig. 32 represents the lingual dentition of an American speci- 



Fig. 32. 



Lingual dentition of LimncBa Juguluris. 



men of Limnsea jugularis. The central tooth is small, narrow, 

 conical. There are 40 r40 teeth, arranged in a transverse, 

 curving row, of variable form. There are 103 rows in all. 



• Rather L. ampla. 



