50 RAMBLES IN SEARCH OF SHELLS. 



below London. An interesting account of the habits 

 of Limncea stagnaUs, and its mode of respiration as 

 observed in confinement, was published some years 

 since by Mr. W. A. Lloyd, in " The Zoologist" for 

 1854, p. 4248. In similar, that is to say marshy 

 situations, are found two species of the genus Physa, 

 or bubble- shell, a peculiar genus intermediate be- 

 tween Planorhis and Limncea. It resembles the 

 former in its long tentacles, and the latter in the 

 form of the shell, but has the spire sinistral. The 

 stream bubble-shell, Ph. fontinalis (PL VI., fig. 5), 

 may be found on watercress and other aquatic plants 

 in streams and canals, and is everywhere tolerably 

 common. The slender bubble-shell, Ph. hypnorum, 

 is rather more local, affecting ponds, ditches, and 

 rank grass in dried-up pools. Both are gregarious, 

 and may be recognized at once by the polished 

 appearance of their shells, the surface of which, 

 being more or less enveloped by an expansion of the 

 mantle, is kept bright by the lubricating friction 

 which it undergoes. The characters by which 

 fontinalis may be distinguished from hypnorum are 

 the oval instead of oblong shell, larger and wider 

 mouth, smaller number of whorls (that is, four or 



