The variations of Peronea caused A. H. Haworth and J. F. Stephens to create 30 or 40 species based on colour and markings. HD was first to be convinced these would be reduced to two.

Discusses species that closely resemble one another;

cites species that differ in variation in different localities;

in some double-brooded species the broods differ markedly in size and colour.

Encloses his list of varieties of Peronea.

Discusses the ranges of alpine species in U. S. and considers the possible migration routes of such species from Europe.

Lists those U. S. genera which he considers protean and describes the U. S. character of some genera which are protean in Europe.

Describes how he distinguishes introduced and aboriginal stocks of the same species.

The species of Mollusca at Mauritius are almost all different from those of surrounding islands, which confirms the belief that the islands were elevated from the ocean rather than separated from the continent by volcanic action.