On the dimorphism of the english species of nummulites, and the size of the megalosphere in relation to that of the microspheric and megalospheric tests in this genus

Abstract

(1) The dimorphism of the English Species of Nummulites . Before the dimorphic character of many of the species belonging to the higher groups of the Foraminifera was established, some of the phenomena dependent on it had been recognised among the fossil nummulites, and attention was called to the different species of Nummulites and Assilina , in the beds in which they abound. It was especially by the careful labours of de Hantken and de la Harpe that this phenomenon was brought to light, and the "Law of the Association of Species in Pairs" was formulated by the latter in his 'Étude des Nummulites de la Suisse' (5, p. 63), as follows:- "Les nummulites apparaissent par couples; chaque couple est formé de deux espèces du même groupe zoologique et de grandeur inégale, la grande est sans chambre centrale, la petite en a toujours une."