PHYSAD^E. 1 1 



what medium they breathe. This resemblance 

 is so apparent, that it would be likely to induce 

 one to believe the genus strictly pneumo- 

 branchiate, without evidence of a contrary 

 nature; and the impossibility of determining its 

 position as a hydrobranchiate mollusc, must 

 have had its influence in retaining it among the 

 Limneans. 



For my own part, whilst I had no right to 

 contradict the respectable authority in favor of 

 free air being the medium of respiration, my 

 own observations convinced me that our Ancyli, 

 at least, breathe water. I found them attached 

 to the lower side of stones, in rapid water, 

 within dead bivalve shells, and in such situa- 

 tions generally, which they could never have 

 attained from the surface. Moreover, I never 

 saw them at the surface of the water, even in 

 vessels under my own eye. I now suspected 

 that, occupying so debatable a ground, the 

 branchiae of this genus might be adapted in- 

 differently to aquatic or aerial respiration, and 

 I was confirmed in this view, by the discovery 

 of a hydrobranchiate Physa (see Physa globosa) 

 in Tennessee.* 



* I would recommend to naturalists to travel in their 



