84 PHTSAD^. 



Subfamily Megasistrophin^, Try mi. 



Megaststropha, Lea.* 



4. Shell dextral, discoidal, whorls visible 

 above and below. 



Subfamily Planorbin^. 

 Aperture unarmed, Planorbis, Guettard. 

 Aperture toothed within, 



Segmentina, Fleming. 



5. Shell non-spiral, conical, patelliform. 



Subfamily Anctlin^. 



* Base or aperture oval, entirely open. 

 Apex directed to the right, 



Ancylus, Geoffroy. 

 Apex directed to the left, 



AcROLOXUs, Beck. 



* Base partly closed by a horizontal lamina. 

 Apex directed backwards, 



GuNDLACHiA, Pfeiffer. 



* Mr. Binney's name Carinifex is generally quoted for 

 this genus, but Mr. Lea's name has priority. It is true that 

 Mr. Binney used the name at an earlier date in some proof 

 sheets, but he requests in the preface that they shall "not 

 be quoted as authority, or referred to as a published work." 

 I yield to Mr. Binney's request. 

 (58) 



