THE NAUTILUS. 91 



Lymnsea stannalis Linn. Canadarago Lake. 



Li/nni/ra columella Say. Allan, Weaver Lakes. 



Lymncea, pa lit 8 tr is Miiller var. Canadarago Lake, Otsego Lake. 



Pbysa ancilluriu Say. Allan Lake. 



Physa IteteiosLiopha Say. Canadarago and Otsego Lakes and 

 many streams. 



Planorbis tnrolvis Say. Allan Lake. 



Planorbis dilatatus Say. Canadaraga Lake. 



Planorbis rampanulatus Say. Canadarago Lake. 



Planorbis bicarinatus Say. Sunset Creek, Canadarago Lake. 



Planorbis exacutns Say. Near Weaver Lake. 



Planorbis tlejleclus Jay. Young's Lake. 



Planorbis albus Miiller. Allan Lake, Otsego Lake. 



Ancylus rivvlaris Say. Oak Creek. 



Ancylus tardus Say. Weaver Lake. 



Ancylus fuscus Adams. Allan Lake. 



Ancylus parallelus Hald. Town Creek. 



Sphariiun simile Say. Sunset Creek, Town Creek, Allan Lake, 

 Weaver Lake. 



Spbcrrium rhomboideum Say. Allan Lake. 



SpbcEiium striatinum Lam. Sunset Creek. 



Pisidium veutricosunt Prime. Canadarago Lake. 



Pisidium novi'lioracensn Prime. Canadarago Lake. 



Lampsilis radiatns Gmelin. Canadarago Lake. 



Slrophitus edrntulus Say. Sunset Creek. 



Anolovta marginuta Say. Weaver Lake. 



Alasnu'douta undulata Say. Sunset Creek. 



Unto complanutus Solander. Oak Creek. 



A NOTE UPON THE INSUFFICIENCY OF THE OFEECfLUM AS A BASIS 

 OF CLASSIFICATION IN EOUND-MOUTHZD SHELLS. 



15Y L. 1\ GKATACAP. 



In 1801 Lamarck established the genus Cyclostoma which lie 

 made for the reception of a very miscellan* oas and unclassified group 

 of shells, characterized however by certain common features as 

 the entire round aperture, continuous peristome, and operculum. 



