INDEX. 243 
Umbilicated shells, 45. 
Umbo of shells, 11. 
Umbonal cavity, 12. 
Unio margaritiferus, 26 ; pearls of, 28 ; ms fisheries of, 29. 
pictorum, 26. 
tumidus, 26. 
Unionide, character of the family, 25 ; genera of, 1b. ; ex- 
tinct species of, 7b. 
Univalve shells, 44. 
Utility of classification, 7 
V. 
VALVATA CRISTATA, 59 ; gills of, 60. 
piscinalis, 58 ; lingual ribbon of, 2b. 
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. 
—— pygmea, 160. 
substriata, 162. 
Vitrina, characters of the genus, 100. 
pellucida, 100 ; voracity of, 101. 
