- The eurypterid fauna of Condroz, Upper Devonic of Belgium.
- Pterygotus problematicus, occurrence doubtful in Aymestry limestone.
- Eurypterus punctatus fragments, Wenlock limestone, England.
To the second belong:
- Strabops thacheri, Potosi limestone, Upper Cambric or Lower Ordovicic.
- Eurypterus prominens, Clinton.
- E. boylii, Guelph.
- E. microphthalmus, Manlius; Monroe.
- Pterygotus problematicus, May Hill sandstone, Llandovery.
- Eurypterus sp. Wenlock (of Southern Belt, Scotland).
- Eurypterus sp. Wenlock (Girvan area, Scotland).
- Pterygotus australis. Upper Siluric of Australia (Information insufficient, may belong to group 1).
- Pterygotus osiliensis, Pterygotus marl of Gotland.
To the third group belong:
- The Siluric fauna of Bohemia.
- The Lockport fauna of Ontario.
- The Siluric fauna of Podolia and Galicia probably belongs here.
- Pterygotus sp. Siemiradzki, Middle Devonic of Galicia.
The lines of argument for the above occurrences have been stated from time to time, but are scattered throughout the paper. They may be brought together here for reference since so many of the cases are subject to the same arguments. In chapter III the criteria for recognizing the various types of habitats in the past were fully discussed, and will now be of great help in establishing the nature of the habitat indicated by the various eurypterid occurrences given in the three lists above. In the light of the arguments that have gone before, and especially of the discussion on habitats, the following truths may be considered as self-evident or as easily demonstrable.
1. The occurrence of a single fragment, or of two or three fragments, or of a single complete eurypterid in a formation where it is associated either intimately in the same stratum or closely in adjoining strata with a typical marine fauna, as defined on p. 76, cannot be considered as proof that the eurypterid remains are a part of the marine fauna, for the following reasons: (a) it is impossible to explain how any group of marine organisms could have their remains so completely destroyed that but a single fragment should be left; such is
