EEPOET OM THE FOEAMIMIFEEA. 
209 
Prof. W. C. Williamson 1 and Dr. Carpenter 2 for the details of its structure and 
morphology. 
Orbiculina adunca, Fichtel and Moll, sp. (PI. XIY. figs. 1-13). 
Nautilus orbiculus, Fichtel and Moll, 1803, Test. Micr., p. 112, pi. xxi. 
„ angulatus, Id. Ibid. p. 113, pi. xxii. 
„ aduncus, Id. Ibid. p. 115, pi. xxiii. 
Archaias spirans, Montfort, 1808, Concb. System., vol. i. p. 190, 48 e genre. 
Hclenis spatosus, Id. Ibid. p. 194, 49® genre. 
Ilotus rotalitatus, Id. Ibid. p. 198, 50® genre. 
Orbiculina adunca, Lamarck, 1816, Tab! Encycl. et Mdth., pi. cccclxviii. fig. 2, a. b..c. 
„ nummata, Id. Ibid. pi. cecclxviii. fig. 1, a.-d, 
„ numismalis, Id. 1822, Anim. s.' Vert., vol. vii. p. 609, Mo. 1. 
„ angulata. Id. Ibid. p. 609, Mo. 2. 
„ uncinata, Id. Ibid. p. 609, Mo. 3. 
„ numismalis, d’Orbigny, 1826, Ann. Sci. Mat., vol. vii. p. 305, pi. xvii. figs. 8-10; — 
Module, Mo. 20. 
,, adunca, Id. 1839, Foram. Cuba, p. 81, pi. viii. figs. 8-14. 
„ compressa, Id. Ibid. p. 73, pi. viii. figs. 4-7. 
Fichtel and Moll, with less than their usual discrimination, figure specimens of this 
species under three different names ; whilst d’Orbigny, not generally given to the 
simplification of nomenclature, recognises the true relationship of the different forms, and 
groups together the Nautilus angulatus, orbiculus, and adunca of the authors referred 
to, as the “ very young,” “ young,” and “ adult ” condition of the same species. He 
stops short, however, at the spiral varieties, and fails to perceive how slight is the modi- 
fication involved in the addition of a few annular chambers to the already nearly discoidal 
shell, and distinguishes the circular or nearly circular specimens by a separate name, 
Orbiculina compressa. 
The fact is, that wherever Orbiculince abound the whole range of contours figured in 
PI. XIV. may almost always be met with— the embracing or involute spiral, the 
explanate or evolute, the crosier-shaped, the fan-like, and the discoidal, together with 
an infinite number of gradational stages. From end to end they present an unbroken 
series and make but a single species. The various modifications bear no relation to 
locality, latitude, or depth of water, and it is quite impossible to make them up into 
groups of any zoological value, or with the slightest basis for subvarietal distinction. 
Orbiculina adunca is an essentially tropical species, and though frequenting com- 
paratively shallow water, or even littoral sands, it flourishes also at considerable depths. 
At four of the Challenger localities the depth ranges from 350 to 450 fathoms. 
It is common about the Cape de Verde Islands, the Bermudas, and amongst the 
1 Trans. Micr. Soc. Land., ser. 1, vol. iii. p. 105. 
2 Phil. Trans., 1856, pp. 547-552; and Introd. Foram., pp. 93-99. 
