234 INDEX. 
Cyclas cornea, 34; varieties of, 2b.; parasite of, ab. 
flavescens, 34. 
— lacustris, 36. 
— ovalis, 36. 
— pisidioides, 35. 
rivicola, 33. 
Cyclostoma elegans, 220 ; peculiar organ in, 221 ; restriction 
of, to limestone soils, 222 ; in a subfossil state, 223. 
D; 
Decollation of spire of shells, causes of, 185. 
Dextral shells, 45. 
Digestive organs of, bivalves, 14 ; snails, 48-52, 93. 
Dimyary bivalves, 18. 
Disappearance and reappearance of water snails, 192. 
Dispersion of water snails, 188. 
Dissection of bivalves, 13. 
Dorsal region, 10. 
Driessena polymorpha, 20; foot, byssus, and apertures of 
mantle of, 21; discovery of, «b. ; introduction of into 
Britain, 22 ; action of light on, 23. 
E. 
EDIBLE SNAILS, 116, 134. 
Entire aperture of shells, 45. 
Epidernus of shell, 11. 
Epiphragm of land snails, 96. 
Equilateral shells, 11. 
Equivalve shells, 10. 
Eyes of bivalves, 17 ; of water-breathing snails, 52; of land 
snails, 92. 
F. 
Foon of bivalves, 19 ; of water-breathing snails, 53. 
Foot of bivalves, 17, 32; of Zebra mussel, 21 ; of water- 
breathing snails, 46 ; of Cyclostoma elegans, 221. 
