18 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
Gallery X. 
Table-case 
16. 
Wall-case 
9b. 
many of the PolythalaTnia were suppo.sed to belong to the 
Cephalopoda, that Class of Mollusca wliich contains the 
nautilus and aniniouite with coiled and chamliered shells so 
like those of soTue loraininifera, but on fin enormously 
larger scale (.see p. 151, Fig. 82). A. D. d’Orbigny, however, 
whose attention liad been directed to the shells found by his 
father in the sea-sand near Rochelle, and who had studied 
similar sands and fossiliferous deposits from various parts of 
the world, published a memoir in 182G, pointing out that 
these microscopic forms dilfered from the true Cephalopoda 
in haying no tube or siphuncle passing through the chambers, 
but simply one or many holes or foramina through the walls 
or septa that separate one chamber from the next ; he there- 
fore distinguished them as “ Foraminiferes ” (hole-bearers). 
By observation of the living animal, Dujardin in 1835 
discovered the more essential difference that, whereas the 
body of a nautilus is an elaborate structure confined to the 
last-formed chamber of the shell, the body of a chambered 
Foraminifer fills every chamber and is of simj)le proto|)lasm, 
connected throughout. Thus the flinty casts of the chambers 
of some Foraminifera found in the flint-meal of Chalk flints 
represent the form of the original animal, without the 
pseudopodia (Fig. 2 h). 
The diversity of form assumed by the shell may be 
studied in the two series of pla.ster models shown on the top 
shelf of the Wall-case. One of these series was made by 
A. 1). d’(.)rbigny and issued to his subscribers, about 1825, 
in four “ Livraisons ” or sets of twenty-five each. The label 
sent therewith described them as “Models of microscopic 
cephalopods, recent and fossil, representing one example 
from each of the chief divisions of a new classification based 
on the mode of growth of the shell. The diameter of these 
models is from 40 to 200 times that of the original shells. . . . 
The coloured models represent the fossil shells ; the white 
models, the recent shells. The position and shape of the 
siphuncles [the openings between the chambers] are indicated 
by the marks or black spots.” The models are labelled with 
the names originally attached to them by d’Orbigny, and are 
arranged in the numerical order in which he sent them out. 
Unfortunately that order was one of pure convenience and 
did not correspond with his classification ; it is, however, the 
order followed in a subsequent description of the models and 
revision of their names by W. K. Parker, T. Rupert Jones, 
and H. B. Brady (Annals and Mag. Nat. Hi.st., July, 1865). 
