258 STUDIES, SCIENTIFIC AND SOCIAL chap. 



genera of European Heteromera from Madeira should be 

 the genus Meloe, is, therefore, one of those critical facts 

 which almost demonstrate that it is not to land-continuity 

 with the continent that the island owes its insect fauna. 



Timarcha. This, the only important apterous genus of 

 Chrysomelidse, is especially abundant in Spain and Algeria, 

 and possesses forty-four South European and North 

 African species ; yet it is unknown in Madeira. 



The occurrence of two isolated European species of 

 characberistic Atlantic apterous genera — Tarphius and 

 Hegeter — may seem to favour the opposite theory. The 

 Tarphius gibbuhis occurs in Sicily, and is the only European 

 species of the genus, of which about forty inhabit the 

 Atlantic islands. It is most nearly allied to the smallest 

 of the Madeiran species, T. Lowei, which is abundant 

 among lichen on weather-beaten rocks and even ascends 

 in the forest regions to the highest branches of the trees. 

 These habits, with its minute size, are all in favour of this 

 species, or some ancestral allied form, having been carried 

 across hj the winds or waves, thus transferring to Europe 

 one of the peculiar types elaborated in the Atlantic isles. 

 The Hegeter tristis is an analogous case, this species of an 

 otherwise exclusively Atlantic genus having occurred on 

 the opposite coast of Africa. These instances will furnish 

 a reply to one of Mr. Murray's difficulties, — that all the 

 migration has been in one direction, from Europe to 

 Madeira, never from Madeira to the continent, — a difficulty, 

 it may be remarked, which is wholly founded on an un- 

 proved and unprovable assumption ; for how can it be 

 determined that, in the case of Acalles for example, the 

 genus had not been first developed in the Atlantic islands 

 and then transferred to Europe, instead of the reverse ? 

 It is always assumed to have been the other way, but I 

 am not aware that any proof can be obtained that it was 

 so, and it is inadmissible to take this unproved assumption, 

 and base an argument upon it as if it were an established 

 fact. 



We will next consider the facts presented by the dis- 

 tribution of those species of Coleoptera which range from 

 Madeira to Europe, or to any of the other Atlantic islands. 



