III.—Tertiary Foraminiferal Limestones from Sinai

Extract

Preliminary remarks on the genus.—The interesting observationson the dimorphism of the genus Nummulites, which have been madefrom time to time by special investigators, such as Von Hantken, Munier-Chalmas & Sohlumberger, De la Harpe, Bupert Jones, andVan den Broeok, have resulted in the establishment of couples of so-called species, constituting a species in the zoological sense, in which the smaller form, with a large central chamber, is referred to as form A, whilst form B usually has a larger test and in variably possesses a diminutive central chamber. The two forms are other-wise spoken of as the megalospheric and microspheric forms. In some cases there may be little doubt as to the accuracy of the assignment of the two forms to one species, especially since they may be the only examples present in the rock. In the case ofa stratum containing more than two species, however, there may be no small difficulty in coupling the actual forms which constitute the species, for there is often little in either the internal or external characters to guide one in linking the forms. In our present state of knowledge, therefore, it appears to be most convenient to describe the forms under their specific denominations as already known, at the same time pointing out their relationship to one another. Some good suggestions as to the naming of Nnmmulites and other Foraminifera which exhibit the two modes of growth and shell form have lately been made by Dr. A. Silvestri.