REPORT OR THE FORAMIHIFERA. 
655 
Planorbulina, d’Orbigny {emend. Carpenter, Parker, and Jones). 
Planorbulina, Truncatulina, Anomalina, Siphonina , et Planulina, auctorum. 
In its full generic significance the term Planorbulina embraces too large an array of 
closely related forms to be conveniently handled as a single group. To obviate the 
difficulties attendant on the collective treatment of so extensive a series, Dr. Carpenter 
and his colleagues recognise the d’Orbignian genera Planorbulina , Truncatulina , and 
Anomalina as representing three subordinate types of sub-generic or quasi-generic value, 1 
and a similar course has been pursued by von Reuss. 2 
Under this arrangement Planorbulina comprises the outspread varieties, the earlier 
segments of which (in typical specimens) are arranged on a piano-spiral plan, whilst those 
subsequently formed are disposed in more or less regular annuli; and the individual 
chambers have marginal orifices, of which those of the outermost whorl constitute the 
general aperture of the test. 
To Truncatulina are allotted the more distinctly Rotaliform species, spiral throughout, 
either plano-convex in contour, the whole of the segments being visible on one side, and 
only those of the final convolution on the other, or else biconvex, the convolutions 
embracing each other to a greater or less degree, though unequally, on both faces 
of the test. 
Anomalina, on the other hand, includes those forms in which the spire not only 
approaches something like bilateral symmetry, but is, at the same time, more or less 
evolute, the contour of the shell being either biconcave and coronate or nearly complanate. 
The genera Siphonina of Reuss and Planulina of d’Orbigny appear needless additions 
to the nomenclature. Hitherto they have each been represented by a single specific form, 
which may be assigned in the one case to Truncatulina and in the other to Anomalina. 
Am ongst Rotalince the genus Planorbulina is characterised typically by the coarsely 
perforated test, and by the aperture which has often a thickened lip or rim, developed 
in some cases to such an extent as to become a short, oval or rounded neck. The 
exterior of the shell is most frequently smooth, but it is subject to superficial decoration 
in the form of limbation of the sutures, exogenous tubercles, or a fringed ccndition 
of the margin. 
The genus Planorbulina, in one or other of its modifications, is common to the seas 
of all latitudes, and its bathymetrical range extends from the littoral zone down to 3000 
fathoms or perhaps more. Its distribution, from the geological standpoint, dates back as far 
as the Carboniferous epoch ; it is rare in the Lias, but becomes comparatively abundant 
during the Cretaceous period, and furnishes a fair proportion of the Rotaline species of 
every division of the Tertiary system. 
1 Introd. Foram., p. 206. 
2 Das Elbthalgebirge in Sachsen, 2'" Theil, p. 113. 
