656 
THE VOYAGE OF H.M.S. CHALLENGER. 
Planorbulina (s. str.), d’Orbigny. 
Planorbulina, d’Orbigny, [1826], Bronn, Munster, Roemer, Hagenow, Reuss, Costa, Williamson, 
Parker and Jones, Carpenter, Karrer, Brady, M. Sars, Fischer, Schulze, Terquem, &c. 
The test of Planorbulina, using the term in its limited sense, has the form of a com- 
planate or somewhat plano-convex disk, which under ordinary circumstances grows 
attached to algse, fragments of shell, or other foreign bodies. It consists typically of a 
single layer of chambers, the whole of which are seen on both faces of the test. In the 
early stage the segments are arranged in a depressed spire, each segment having an orifice 
at its inner peripheral margin ; subsequently the mode of growth becomes more or less dis- 
tinctly cyclical, the segments of the successive annuli alternating with each other. In this 
later stage the individual segments have two small lipped orifices, one at each extremity, 
close to the line of union with the previous whorl ; and the adjacent orifices of each two 
chambers open into the intermediate segment of the next annulus ; whilst those of the 
outermost row appear externally and form collectively the general aperture of the test. 
Morphologically the attached side of the shell is its superior face. 
A departure from the typical plan of growth is exhibited by certain acervuline 
varieties, in which a number of small chambers, crowded together without order or 
regularity, cover the free or inferior face of the shell. 
Planorbulina most affects the shallow-water margins of the seas of temperate and 
tropical latitudes. At depths greater than 100 fathoms the genus becomes rare, but it 
has been taken as low as 600 fathoms, and in one locality down to 1125 fathoms. Its 
earliest appearance as a fossil is at about the middle of the Tertiary epoch, and it is not 
uncommon in later Tertiary formations. 
Planorbulina mediterranensis, d’Orbigny (PL XCII. figs. 1-3). 
“ Corpuscula plano-papillosa, ” Soldani, 1795, Testaceographia, vol. i. pt. 3, p. 238, pi. clxi. 
figs. E.F.G-. — pi. clxii. fig. H. 
Planorbulina mediterranensis, d’Orbigny, 1826, Ann. Sci. Nat., vol. vii. p. 280, pi. xiv. figs. 4-6; — 
Modele, No. 79. 
,, vulgaris, Id. 1839, Foram. Cuba, p. 85, pi. vi. figs. 11-15. 
„ „ Id. 1839, Foram. Canaries, p. 134, pi. ii. fig. 30. 
,, „ Williamson, 1858, Rec. For. Gt. Br., p. 57, pi. v. figs. 119, 120. 
„ farcta, var. mediterranensis, Parker and Jones, 1865, Phil. Trans., vol. civ. p. 383, 
pi. xvi. fig. 21. 
,, mediterranensis, Parker, Jones, and Brady, 1871, Ann. and Mag. Nat. Hist., ser. 4, 
vol. viii. p. 178, pi. xii. fig. 133. 
The common typical species of Planorbulina has a thin, outspread shell, the superior 
or attached surface of which is fiat, or nearly so, and the inferior uneven and lobulated, 
