240 INDEX. 
Pp. 
PAINTERS’ MUSSEL, structure of, 10; description of, 26. 
Paludina Listeri, 56. 
vivipara, 54; effects of cold upon, 56. 
Pearls of Unio margaritiferus, Mytilus edulis,28; Avicula 
margariefera, vb. ; nature of, 2b.; artificial production 
of, 2b. ; 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, 2b.; geological distribution of, 211 ; synoptical table 
of species of, 2b. 
—— albus, 216. 
— carinatus, 216. 
—— complanatus, 216. 
—— contortus, 213. 
—— corneus, 212; pellicle formed by, 213. 
—— olaber, 217. 
—— helicoides, 211. 
—— imbricatus, 218. 
—— lineatus, 219. 
—— marginatus, 215. 
—— nautileus, 217. 
—— nitidus, 218. 
