742 
THE VOYAGE OF H.M.S. CHALLENGER. 
Fossil specimens corresponding with the forms under notice have been observed in 
the .Eocene deposits of the Paris Basin (Terquem), and in the Upper Eocene of the Swiss 
Alps (Kaufmann) ; and they abound in the Miocene and Pliocene strata of Austria, the 
south of France, the south-east of Spain, Italy, Malta, Costa Rica, Jamaica, San Domingo, 
Trinidad, Maryland, Virginia, South Carolina, Alabama, Australia, and New Zealand. 
Operculina, d’Orbigny. 
Nautilus , pars, Gronovius [1781], Schroeter, Gmelin. 
Lenticulites, pars, Defrance [1822], Basterot. 
Operculina , d’Orbigny [1826], Bronn, Michelotti, Reuss, Leymerie, Cornuel, Riitimeyer, 
dArchiac and Haime, Carter, Parker and Jones, Carpenter, Brady, M. Sars, Kaufmann, 
Hantken, &c. 
Amphistegina, pars, d’Orbigny [1826], Reuss. 
Nonionina, pars, Williamson [1852], Fiscber. 
Nummulina , pars, Parker and Jones [1865]. 
The test of the typical Operculina is a thin complanate disk, composed of three or 
four broad convolutions, symmetrically arranged, and equally visible on both faces. The 
central portion of the disk is usually somewhat thicker than the outer whorls, and not 
unfrequently almost umbonate ; the earlier convolutions are more or less embracing, the 
later whorls evolute. The segments are usually very numerous, of gradually increasing 
size, and typically very short in the direction of growth as compared with their width 
radially ; they are for the most part produced on a uniform plan, but near the finish 
are often irregular, both as to shape and size (PL CXII. figs. 3, 4, and 6). The exterior 
is sometimes smooth ; but more frequently either the sutures, or the surface of the 
chambers, or both, are ornamented with exogenous granules, papillse, or tubercles, which 
as a rule are more strongly developed near the centre than on the later whorls ; and 
in the small, northern variety of the genus, the septal lines and periphery are distinctly 
limbate. The general aperture is a straight or slightly curved fissure at the inner margin 
of the final segment, close to the periphery of the previous convolution ; but the test 
has frequently also a number of secondary orifices, in the form of small circular pores on 
the face of the terminal segment. The septa are double, and the skeleton is furnished 
with a system of canals, the general features of which are analogous to that of 
Nummulites. 
Excepting the genus Nummulites, there is probably no foraminiferal type that has 
been the subject of so large an amount of careful investigation as Operculina, 1 and a 
very complete exposition of what is known of its structure and organisation is given in 
the Introduction to the Study of the Foraminifera. 
1 See Williamson, 1852 , Trans. Micr. Soc. Lond. ( 1850 ), ser. 1 , vol. iii. p. 105 [ Nonionina .] Carter, 1852 , Ann. and 
Mag. Nat. Hist., ser. 2 , vol. x. p. 161 . Carpenter, 1859 , Phil. Trans. ( 1858 ), p. 12 ; — 1862 , Introd. Foram., p. 161 . 
