INDEX. 
243 
U. 
Umbilicated shells, 45, 
Umbo of shells, 1L 
TJmbonal cavity , 12. 
Unio margaritiferus, 26 ; pearls of, 28 ; pearl fisheries of, 29. 
- pictorum, 26. 
- tumidus, 26. 
Unionidae, character of the family, 25 ; genera of, ib. ; ex¬ 
tinct species of, ib. 
Univalve shells, 44. 
Utility of classification, 7. 
V. 
Valvata cristata, 59 ; gills of, 60. 
—— piscinalis, 58 ; lingual ribbon of, ib. 
Valves , 10. 
Varieties of species, 6. 
Velletia, 205. 
- lacustris, 208. 
Ventral region , 10. 
Vertebrate animals, 2. 
Vertigo, characters of, synoptical list of species of, 158. 
- alpestris, 161. 
- antivertigo, 161. 
- angustior, 163. 
- edentula, 159. 
- minutissima, 159. 
-Moulinsiana, 162. 
-palustris, 161. 
- pusilla, 163. 
- pygmaea, 160. 
-substriata, 162. 
Vitrina, characters of the genus, 100. 
- pellucida, 100 ; voracity of, 101. 
