REPORT OH THE FORAMINIFERA. 
391 
Valvulina, d’Orbigny. 
Valvulina, d’Orbigny [1826], Munster, Bronn, Reuss, Parker and Jones, Earrer, Carpenter, 
Brady, M. Sars, Robertson, Schulze, Berthelin, &c. 
Tetrataxis, Ehrenberg [1854], Moller, Schwager. 
Rotalina, pars, Williamson [1858], Parfitt, Terquem. 
Valvulina triangularis, the species portrayed in d’Orbigny’s Model No. 25, has 
been selected by Parker and Jones as the type of a large group of closely-related 
Foraminifera. The model in question represents a triserial shell, compressed on three 
sides, and with sharp salient angles, broad and somewhat rounded at the oral end, 
and tapering to a point at the opposite extremity, the aperture, which is situated on 
the inner margin of the final segment, being partially covered by a projecting flap or 
valve. 
Modifications of this typical structure take place in two directions. Cn the one hand, 
the test, whilst preserving the normal arrangement of the chambers and the characteristic 
aperture, loses its angular contour and becomes conical or even plano-convex, producing 
forms like Valvulina conica and Valvulina fusca ; and a further slight deviation from the 
type occurs "in certain fossil species of Palaeozoic age, which frequently exhibit more than 
three segments in each whorl. 
On the other hand, the typical structure modified in the opposite direction, that is 
to say, becoming elongated and columnar instead of widening laterally, furnishes a series 
of dimorphous forms, in which the earlier chambers preserve the normal triquetrous 
arrangement, whilst the later ones are disposed in a uniserial line. These varieties, 
which constitute the subordinate genus Clavulma, assert their relationship by retaining 
the valvular aperture even in the uniserial segments. 
The test of Valvulina is invariably more or less arenaceous ; but unlike that 
of the Lituolid'zE, it often possesses a well-defined, perforate, shelly basis or lining, 
which is sometimes exposed to view where the exterior has been abraded. The 
same sort of structure has already been referred to in connection with the allied genus 
Textularia. 
The geographical distribution of the genus Valvulina is exceedingly wide, in fact the 
type is met with, in one form or other, in all the great oceans, though seldom at depths 
of more than five or six hundred fathoms. In the fossil condition it dates back as far as 
the Carboniferous epoch, having furnished one of the most important groups of minute 
Foraminifera occurring in the limestones of that age ; but it is better known as a Tertiary 
genus, conspicuous in the Eocene deposits of Grignon and Hauteville. 
