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Pleurotomaria granulata, Sowerby. Ferruginous Oolite, Normandy. Pleurotomaria ornata, Sowerby Sp. Ammonites Humphresianus, Sowerby. Ammonites Braikenridgii, Sowerby. Oolite, Scarborough. Ostrea Marshii. One-half natural size. The extinct genus Pleurotomaria is also a form very common in this division as well as in the Oolitic system generally.
To this subject I shall refer again when treating of the metamorphic rocks, and of the slaty and jointed structure. Phasianella Heddingtonensis, and cast of the same. Pleurotomaria Anglica, and cast. The changes which fossil organic bodies have undergone since they were first imbedded in rocks, throw much light on the consolidation of strata.
Even Pictet, in the second edition of his Paleontology, still considers Pleurotomaria as extinct, and as belonging to the fossiliferous formations which extend from the Silurian period to the Tertiary. Of the living species found at Marie Galante, nothing is known except the specific characteristics of the shell.
Enough to occupy half a dozen competent zoologists for a whole year, if the specimens could be kept fresh for that length of time. The first haul brought up a Chemidium-like sponge; the next gave us a crinoid, very much like the Rhizocrinus lofotensis, but probably different; the third, a living Pleurotomaria; the fourth, a new genus of Spatangoids, etc., etc., not to speak of the small fry.
Pleurotomaria carinata, Sowerby. Mountain Limestone. Euomphalus pentangulatus, Sowerby. Mountain Limestone. a. Upper side. b. Lower or umbilical side. c. View showing mouth, which is less pentagonal in older individuals. d. Euomphalus is a characteristic univalve shell of this period.
It would be just as true to nature to say that the tertiaries are continued in the tropics, on account of the similarity of the miocene mammalia to those of the torrid zone. We have another case in the Pleurotomaria. It is not long since it has been made known that the genus Pleurotomaria is not altogether extinct, a single specimen having been discovered about ten years ago in the West Indies.
Charles Peach was the first to find, in 1854, three or four species of Orthoceras, also the genera Cyrtoceras and Lituites, two species of Murchisonia, a Pleurotomaria, a species of Maclurea, one of Euomphalus, and an Orthis. Several of the species are believed by Mr. Salter to be identical with Lower Silurian fossils of Canada and the United States.
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