. The Canadian naturalist and geologist. Natural history -- Periodicals. 1865.] BILLINGS—SILURIAN AND DEVONIAN FOSSILS. 191 therefore, that Eichwald's genus Tetragonis was founded on a species of Receptaculites, with the ectorhin removed. The genus Ischaditcs also exhibits very similar markings, as may be seen by comparing the figures of/. Kcenigii (Murch.), on pi. 12, ' Siluria,' and the following of R. Canadensis. The specimen represented by fig. 10 has been figured by me in the Geology of Canada, p. 304, under the name of Ischadites Canadensis. It is the cast of the inner surface of the ect
. The Canadian naturalist and geologist. Natural history -- Periodicals. 1865.] BILLINGS—SILURIAN AND DEVONIAN FOSSILS. 191 therefore, that Eichwald's genus Tetragonis was founded on a species of Receptaculites, with the ectorhin removed. The genus Ischaditcs also exhibits very similar markings, as may be seen by comparing the figures of/. Kcenigii (Murch.), on pi. 12, ' Siluria,' and the following of R. Canadensis. The specimen represented by fig. 10 has been figured by me in the Geology of Canada, p. 304, under the name of Ischadites Canadensis. It is the cast of the inner surface of the ectorhin, and differs remarkably from the similar specimen of R. Oweni (ante, fig. 7). It is deeply pitted all over with sub-quadrangular or rhomboidal depressions, the form of each cavity being such as would be made by the impression of a small four-sided pyramid. In the bottom of each is a small rounded orifice, from which radiate three grooves to three of the angles of the square. These,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Natural History Society of Montreal. Montreal, Dawson
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