GENUS ORBITOLITES. 105 



Genus X. — Orbitolites (Plate IX). 



154. Ilistori/. — The Orbitolile has been chiefly known, until very recently, rather by its 

 fossil than by its existing forms. The abundant occurrence of its disks in the ' Calcaire 

 grossier ' of the Paris basin early attracted attention ; but Orbitolites were not clearly distin- 

 guished by the older observers from Nummulites, and their true nature was entirely misun- 

 derstood. Thus we find them designated, often in association with Nummulites, under the 

 title of UmbiUcus marinm by Plancus (lxxxiii), who imagined them to be opercula of 

 Ammonites ; of Porpitce nummulares by Stobaeus and Bromell, who seem to have regarded 

 them as representing the disks of the existing Porpitae ; of Helicilcs and Operculites by 

 Guettard, who considered them as opercula of Gasteropods ; of BiscolUhi by Fortis, who 

 supposed them to be skeletons of Mollusks ; of Madreporites by Deluc, and of MiJleporites 

 by Faujas de St. Fond, whose idea of their nature is sufliciently indicated by the names they 

 assigned to them. (See i, § i.) The genus Orbitolites seems first to have been erected on 

 the type of the 0. coMplanafa of the Paris basin, and to have been differentiated from 

 Nummulites, by Lamarck (lviiJ, who ranked it between Lmmlites and Millepora, among his 

 " Polypiers Foramines." He subsequently (lx) altered the name from Orbitolites to Orbic- 

 Hies ; but the latter designation having been previously employed in Malacology, the first 

 appellation was restored by M. Milne Edwards in his posthumous edition of Lamarck's 

 work. Under one of the designations Orbilolites or Orbulites, the genus has been gene- 

 rally recognised by systematists (xiii) ; none of them, however, have either given any 

 account of its internal structure, or made any essential modification in the definition of the 

 genus ; and they all left it in the place which Lamarck had assigned to it, until after the 

 appearance of my own description of the microscopic structure of Orbitolites (xii), in which 

 I showed its identity with the recent Australian Maryinopora of MM. Quoy and Gaimard, 

 and of the subsequent memoir by Prof. Williamson (cviii), in which the Foraminiferous 

 character of this type w'as proved by the close conformity of its plan of organization to 

 that of Orbicnlina* It was not until the publication of his ' Cours Elementaire' (lxxiv) 

 in 18.52, that M. D'Orbigny admitted this genus into his systematic arrangement of Fora- 

 minifera ; the order Cyclostjigues, in which it is associated with Cyclolina (which I believe 

 to be only a variety of Orbitolites), with OrbiloUna (a generic type of quite a different 

 structure, to which I have thought it better to restore De Montfort's name Tinoporus), and 

 with Orbitoides (whose affinities with Cyclocli/pem and Kumiiiulilcs are of the most intimate 

 character), being then first created. 



* It is due to Prof. Ehrenberg to state tliat he liad long before recognised this relationship 

 (xxxix) ; but by ranking Orbicidbia as well as Orbitolites among Bnjozoa, and by representing the 

 superficial cells in both types as occupied by eiglit-aruied polypes furnished with moveable opercula, 

 he so completely departed from the truth of nature, that it is not surprising that what was really correct 

 in his doctrines received little attention. 



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