_General Conclusions as to the Neotropical Insect-fauna._--Looking at the insects of the Neotropical region as a whole, we are struck with the vast amount of specialty they present; and, considering how many causes there are which must lead to the dispersal of insects, the number of its groups which are scattered { 19}over the globe is not nearly so great as we might expect. This points to a long period of isolation, during which the various forms of life have acted and reacted on each other, leading to such a complex yet harmoniously-balanced result as to defy the competition of the chance immigrants that from time to time must have arrived. This is quite in accordance with the very high antiquity we have shown most insect-forms to possess; and it is no doubt owing to this antiquity, that such a complete diversity of _generic_ forms has been here brought about, without any important deviation from the great _family_ types which prevail over the rest of the globe.
_Land Shells._--The Neotropical region is probably the richest on the globe in Terrestrial Mollusca, but this is owing, not to any extreme productiveness of the equatorial parts of the continent, where almost all other forms of life are so largely developed, but to the altogether exceptional riches of the West India Islands. The most recent estimates show that the Antilles contain more species of land shells than all the rest of the region, and almost exactly as many as all continental America, north and south.
Mr. Thomas Bland, who has long studied American land shells, points out a remarkable difference in the distribution of the Operculated and Inoperculated groups, the former being predominant on the islands, the latter on the continent. The Antilles possess over 600 species of Operculata, to about 150 on the whole American continent, the genera being as 22 to 14. Of Inoperculata the Antilles have 740, the Continent 1,250, the genera being 18 and 22. The proportions of the two groups in each country are, therefore:
Operculata Gen. 22 Sp. 608 14 151 Inoperculata " 18 " 737 22 1251
The extensive family of the Helicidæ is represented by 22 genera, of which 6 are peculiar. _Spiraxis_ is confined to Central America and the Antilles; _Stenopus_ and _Sagda_ are Antillean only; _Orthalicus_, _Macroceramus_, and _Bulimulus_ have a wider range, the last two extending into the southern United { 20}States. Important and characteristic genera are, _Glandina_, in all the tropical parts of the region; _Cylindrella_, in Central America and the Antilles; _Bulimus_, containing many large and handsome species in South America; _Stenogyra_, widely spread in the tropics; and _Streptaxis_, in Tropical South America.