GENUS ORBICULINA. 93 



Peneroplis and Spirolina, to the exclusion of Bendritina ; whilst in the Vienna Tcrtiaries we 

 meet with Dendritinn and Spirolina, to the exclusion of Peneroplis. 



GenusX. — Orbiculina (Plate VIII, figs. 1 — 12) 



134. History. — The interesting group of organisms belonging to this type seems to 



have early attracted notice, probably on account of the great abundance in which it presents 



itself on the sands of many of the West Indian shores. Three species are described 



and figured by Fichtel and Moll (xlv), under the ^ames oi Nautilus orbictdus, N.anr/ulatus, 



and N. aduncm. Lamarck (lix), however, separated them from Nautilus, and raised them 



to the rank of an independent genus, to whicii he gave the name of Orbiculina ; and he also 



changed two of the specific names, the three standing respectively as 0. numismalis, 



0. angulata, and 0. uncinata. By Montfort (lxvii), these species were raised to the rank 



of independent genera, under the names of Helenis, Archaias, and Hates ; but these genera 



have not been adopted by any other systematist. M. d'Orbigny, in his first classification of 



the Foraminifera (lxix), not merely adopted Lamarck's generic designation, but afiirmed 



that the three reputed species were really nothing else than one and the same organism in 



difi"erent phases of growth, 0. angulata being the youngest, 0. numismalis the next in age, and 



0. 7incinata the adult. He arrived at this result, of the truth of which I am myself well 



assured, by the comparison of a great number of specimens, a process which it would have 



been well for science if he had more constantly adopted. The name of the adult form 



should, of course, stand as that of the species; but the organism in question is more commonly 



known under the designation Orbiculina adunca, which seems to have been conferred upon it 



by M. Deslongchamps (xxxii). A considerable number of figures of this species are given 



by M. d'Orbigny in his treatise on the Foraminifera of Cuba (xcii) ; they serve only, 



however, to give a general idea of the diversities of external conformation which had 



presented themselves to him ; and notwithstanding their number and variety, they do not 



include some of the most important among the protean shapes of these bodies, nor do they 



throw any light upon their internal structure- The memoir of Prof. Ehrenberg, in which 



his group of Bryozoa was originally constituted (xxxix), contains the first recognition of the 



near relationship between Orbiculina and Orbifolites, which he grouped in close proximity 



among the Bryozoa. His description of their structure, however, is so greatly prejudiced 



by his erroneous idea of the nature of the animal body to which they belonged, and is 



rendered so imperfect by his want of acquaintance with the appearances presented by their 



sections, that it serves rather to mislead than to infoi'm any one who may consult it. It was 



by Prof. Williamson (cviii) that the real structure of OrhicuUiia, and its very close conformity 



to that of Orbitolites as previously described by myself (xii), were demonstrated ; and that 



the frequent exchange of the spiral for the cyclical plan of growth, witli the advance of age, 



was recognised ; and the few slight errors into which he fell are probably attributable to the 



imperfect state of the specimens on which his description was founded. 



