In describing the shell fish supposed to yield the Tyrian dye, Pliny has adverted to its power of boring the shells of other fish; and Lamarck says that all mollusca, whose shells have a notch at the base of their apertures, are possessed of similar powers. In the other genera of turbinated univalves, the aperture, instead of being notched, is entire, and they have all been proved to be herbivorous. Every turbinated univalve which Mr. Dillwyn has examined of the older beds, from the transition limestone to the lias, belongs to these herbivorous genera, and the family still inhabits our land and waters. On the contrary, all the carnivorous genera abound in the strata above the chalk, but are very rare in the secondary strata. In recent shells small holes bored by the predaceous Trachelipoda are common; and Mr. Dillwyn has observed similar holes in fossils from the London clay, but never in those of the older formations; and he thinks that the whole family of carnivorous Trachelipoda are very rare in all those strata where the Ammonites and other Nautilidæ abound. Ammonites, and the other principal multilocular genera, appear to have become extinct in northern latitudes when the chalk formation was completed: but a few of the Nautilidæ still inhabit the Southern Ocean. Mr. Dillwyn further observes, that all the marine genera of the herbivorous Trachelipoda, to which the fossil species belong, have an operculum, and that the carnivorous species of the secondary strata agree with them in this particular, though the unoperculated genera abound in the London clay. Although fossil Nautilidæ are common in the secondary strata of the United States, they are said not to have been found in South America. Hence, says the author, it may be queried whether the Cephalopoda were not confined to the more northern latitudes when the chalk formation was completed; and whether a decrease in the earth’s temperature at that period may not have occasioned the entire destruction of some genera, and the migration of others to the south.
Honor Bridget Fell, 22 May 1900 - 22 April 1986