CLASSIFICATION OF THE FORAMINIFERA. 343 
_ As the mode in which the erowth of the body, and con- 
_ sequently of the shell, takes place, differs greatly in certain 
_ groups, an obvious and natural arrangement is suggested, by 
which the class is divided into seven orders :— 
1. The primary, or simplest type; one segment or cell ; 
as in Orbulina. 
| 2. The segments arranged in circular lines; as in Orii- 
tolina. 
3. Segments disposed in a straight or arched single line ; 
successively increasing from, the first to the last cell; as in 
Nodosaria, Lign. 111. ; 
4, Seoments, spirally and discoidally disposed, on the 
same plane, like cells of the Nautilus; as in Cristellaria, 
Lagn. 109. 
_ The same type, but coiled obliquely, and inequilaterally, 
like the shells of Gasteropoda ; asin Globigerina, Lign. 109, 
Rosalina, Lign. 109. 
5. Segments developed alternately on the right and left 
of the first, and successively on each side the longitudinal 
axis; as in Teatularia, Lign. 109. 
' 6. Arrangement of the segments combining the modes 
_of 4 and 5; that is, the segments are formed alternately, but 
the whole are coiled spirally, either obliquely, or on the 
same plane; as in Amphistigena. 
7. Segments round a common axis, on two, three, four, 
or five, opposite faces, returning after each entire revolu- 
tion; the new cells being placed exactly on the preceding 
series ; as in Quinqueloculina, Pict. Atlas, pl. \xii. fig. 12. 
The Foraminifera vary considerably in magnitude ; by far 
the greater number of species are invisible to the unassisted 
eye, and the aid of a lens or microscope is required to define 
the structure even of the largest; yet many are of sufficient 
size to be recognized, as for example the Spiroline, Lign. 
112. A few genera are from a quarter of an inch to nearly 
an inch in diameter, as the Orbitoides Mantellr of the 
