INDEX. 199 



Eurygnathus Latreillei, Lap., variety of, on one of the Madeira 



Islands, 88, 109. 

 Exceptions, not be allowed to negative a law, 72, 73. 

 Extinction of species, as indicated in the Madeiran Helices, 131 ; 



the only cause by which genera may be abruptly defined, 176. 



Forbes, Prof. E., on the origin of the British animals and plants, 

 130 ; his epochs of migration of the British animals and plants, 

 136 ; on the existence of a former Atlantic continent, 137- 



Forests, the hindrance which they offer to insect-diffusion, 164. 



" Fortunate Islands " of the ancients, probably the Canarian group, 



Galapagos, fauna of, 23. 



Genera, the nature of, often misunderstood, 160; a familiar expla- 

 nation of, 160, 161, 162; cannot be abrupt except trom accident, 

 169; how to be defined, 169; the types of, usually situated 

 towards the centres of the several groups, 17"; the types of, 

 usually eveuly balanced in their structural chai-aeters, 171, 172; 

 may be abruptly defined from accidental causes, 176, 177- 



Generic areas, an important feature throughout Nature, 130, 141, 184. 



Geology, a necessary item in the study of insect-diffusion, 113. 



Germanic plains, the, probably a primary area of diffusion, 130. 



Gerris, on the development of the wings of, 100. 



Gould, Mr., on the Swallows of Malta, 102. 



Gymnaetron, blood-red dashes characteristic of, 62. 



CampanuUs, Linn., its smallness on the Cornish coast, 58. 



Veronica, Germ., a variety of G. niger, 62. 



Hadrus illotus, WoU., perhaps a form of H. cinerascens, 66. 



Haliplus obliquus, GylL, dark state of, in Ireland, 67. 



Haltica exoleta, Fabr., its variability on the coast, 59. 



Harcourt, Mr., on the discovery of Madeira, 49, 50. 



Harpalus vividus, Dej., changes to which it is subject, 67, 68, 69; 

 variable in the connateness of its elytra, 96, 97. 



Hegeter, its maximum attained in the Canaries, 120. 



elongattts, Oliv., its migration from the Canaries, 120; of a 



more adaptive nature than its allies, 121. 



latebricola, Woll., its occurrence in the Salvages, 120. 



Helices, have often two distinct states, 106; many of them repre- 

 sentative in the Madeira Islands, 128, 129 ; those in the Madeiras 

 chiefly of slow migratory powers, 130, 131. 



Helix attrita, Lowe, its local character, 132. 



Bowdichiana, Fer., perhaps a gigantic state of H. punctulata, 



106. 



calculus, Lowe, sedentary nature of, 132. 



