In examining the remarkably fine series of examples of Cœlonautilus cariniferus, mostly from the Carboniferous Limestone of Ireland, contained in the Geological Collections of the British Museum (Nat. Hist.), some were found to exhibit upon the cast of the body-chamber distinct marks of the shell-muscles. In one specimen (No. 50190) these are so perfect as to give a very clear outline of their form, and some of the test having been removed, their entire course can be made out.
3 This name from κολον hollow (referring to the umbilicus), and Nautilus, is proposed by one of us in substitution for Trematodiscus, Meek and Worthen, which was used by Häckel for a genus of Radiolarians. The name Trematoceras proposed by Hyatt (Proc. Boston Soc. Nat. Hist. 1883, vol. xxii. footnote, p. 291) in lieu of Trematodiscus is equally ineligible, because preoccupied, for although the species described by Eichwald (Leth. Rossica, 1860, vol. i. p. 1259)—Trematoceras discors—was a Bactrites, a generic name once publislied cannot be again employed, even for a different group, without risk of confusion.