460 OBSERVATIONS ON THE ANIMALS 
tertiary formations. The recent species are chiefly from the Adria- 
tic, although a few of them are natives of the British coast. 
The shells of D’Orbigny’s second group are not so simple in their 
construction as those we have just described. ‘The chambers do not 
form a regular spire, although that is the apparent shape ; but they 
are placed alternately right and left, piled upon each other on two 
or three distinct axes; sometimes the septum of the right hand 
chambers overlapping more or less those of the other side, and some- 
times merely touching. The apparent spire often resembles that of 
the common univalve shells, Cerithium, Turritella, &c.; but occa- 
sionally it is more rounded, the apex being obtuse and more like the 
shell called “‘Pupa.” There are seven genera referred to this group, 
and between sixty and seventy species: the shell is always porous 
in its structure, and the exterior rough and irregular. More than 
half the species occur fossil, but most of these belong to one genus, 
the Polymorphina of D’Orbigny, characterised by the simple alter- 
nation of the chambers and the roundness of the aperture. Twenty 
out of the twenty-eight species of this genus are found fossil in the 
Paris Basin. Besides this, one other genus has nearly half its spe- 
cies fossil, and one is confined to a single fossil species. 
The third group contains those shells of which the component 
cells are arranged on one, or at most two, distinct axes, but which 
form a decided spiral by their mode of increase, the spiral being in 
some cases elevated, and in others flattened. This group has been 
sub-divided into three sections, which we will consider separately, 
as each contains some of the most remarkable and abundant fossil 
species, a very large proportion of which—as many as one hundred 
and thirty-three—are referred to this important sub-division of the 
Foraminifera. 
The first section comprises ten genera and sixty-two fossil spe- 
cies, all of which have the chambers arranged on a single axis, and 
forming a spire more or less elevated. Some of these have very sin- 
gular shapes, which are perfectly indescribable without the aid of 
accurate models, or at least engravings. The most interesting to 
the geologist of the genera of this section is that called Rotalites— 
the “ Rotalia” of Lamarck and D’Orbigny—which contains thirty- 
two fossil species, chiefly met with in the tertiary beds of Bourdeaux. 
The shell is trochiform and regular ; the spire sometimes prominent, 
sometimes flattened ; and the aperture is a longitudinal slit opposite 
the penultimate whorl, usually unprovided with marginal appen- 
dices, the occurrence of which, however, in some species, has been 
