382 MINUTE MULTILOCULAR SHELLS. 
Genera and species of larger Cephalopods. 
M. D'Orbigny bas noticed from GOO to 700 spe- 
cies of these shells, and has prepared magnified 
models of 100 species, comprehending all the 
Genera.* 
The greater number of these shells are micro- 
scopic, and swarm in the Mediterranean and 
Adriatic. Their fossil species abound chiefly in 
the Tertiary formations, and have hitherto been 
noticed principally in Italy. (See Soldani, as 
quoted at page 117 of this volume.) They occur 
also in the Chalk of Meudon, in the Jura Lime- 
stone of the Charente inferieure, and the Oolite 
of Calne. They have been found by the Marquis 
of Northampton in Chalk flints from the neigh- 
bourhood of Brighton. 
* M. D'Orbigny, in his Classification of the shells of Cepha- 
lopodous MoUusks, has established three orders. 1. Those that 
have but a single chamber, like the shell of the sepia and horny 
pen of the Loligo. 2. Polythalamous shells, which have a 
siphuncle passing through all the internal chambers, and which 
terminate in a large external chamber, beyond the last partition, 
such as Nautili, Ammonites, and Belemnites. 3. Polythalamous 
internal shells, which have no chamber beyond their last par- 
tition. 
Shells of this Order have no siphuncle, but the chambers 
communicate with each other by means of one or many small 
foramina. On this distinction he has founded his Order Fora- 
minifereSj containing five families and fifty-two genera. 
It may be necessary to apprize the reader that doubts have 
been entertained as to the cephalopodous structure of some of 
these minute multilocular shells ; and that there are not wantina' 
those who attribute to them a different organization. 
