240 
INDEX. 
P. 
Painters’ mussel, structure of, 10 ; description of, 26. 
Paludina Listen, 56. 
- vivipara, 54; effects of cold upon, 56. 
Pearls of JJnio margaritiferus, Mytilus edulis ,28; Avicula 
margaritifera , ib. ; nature of, ib. ; artificial production 
of, ib. ; value of, 30. 
Pedal muscles of bivalves, 18 ; of water-breathing snails, 47. 
Peristome of shells, 45. 
Physa (bubble snails), 201. 
-fontinalis, 202 ; modes of progression of, 203. 
- hypnorum, 203 ; movements of, how effected, 204. 
Pisidium (genus), characters of, 38. 
- amnicum, 38. 
-cinereum, 38. 
-Henslowianum, 40. 
- nitidum, 41. 
- obtusale, 42. 
-pulchellum, 39. 
- pusillum, 42. 
Planorbis (coil snails), characters of, 210 ; red fluid emitted 
by, ib.; geological distribution of, 211 ; synoptical table 
of species of, ib. 
- albus, 216. 
-- carinatus, 216. 
-complanatus, 216. 
- contortus, 213. 
- corneus, 212 ; pellicle formed by, 213. 
- glaber, 217. 
-helicoides, 211. 
-imbricatus, 218. 
- lineatus, 219. 
- marginatus, 215. 
-nautileus, 217. 
-nitidus, 218. 
