18 
MOLLUSC A, 
M. D’Orbigny, who has exceeded evei’y other person in attention 
to this subject, forms them into an order which he calls Foraminifera, 
on account of the only communication between the cells being by 
means of holes, and divides them into families according to the man- 
ner in which the cells are disposed. 
AVhen the cells are simple and spirally arranged, they constitute 
liis Helicostegua, which are again subdivided. If the whorls are en- 
veloped, as is particularly the case in the Nummulites, they become 
his Helicostegua nautiloida* * * § . 
If the whorls do not envelope each other, they are the Helicostegua 
ammonoida.] 
If the whorls are elevated as in most Univalves, they are the 
Helicostegua turbin oida.\ 
Simple cells may also be strung upon a single, straight or slightly 
curved axis, constituting the family of the Stycostegua.^ 
* These infinitely small beings having but little to do with our plan, we will 
merely cite the names of the genera with a few examples. The Nummulites them- 
selves are compressed in this first division under the name of Nummu lines, — 
Nautilus pompilo'ides, Ficht., and Moll., N. mcrassatus, Id. 
The Syderolina, the same as Syderolites, Lam. 
Cristellaria, — Nautilus cassis, Naut. galea, Id., &c. 
Robulina, Nautilus calcar, Naut. vortex, Id. 
Spirolina, — Spirolinitcs cylindracea, Lam. Anini., sans verteb, 
Peneropla, — Nuutihis 2itanah(s, Ficht. and Moll., &c. 
Dentritina, 
POLYSTOMELLA, 
Anomalina, 
Vertebralina, 
Cassidulina. 
•f M. D’Orbigny divides them into four genera ; 
SOLDANIA, 
Operculina, 
Planorbulina, 
Planulina. 
These form ten genera ; , 
Truncatulina, 
Gyroidina, 
Globigerina, 
Calcarina, where is placed, among others, the Naxitilus Spengleri, Fich. and 
Moll. XIY, d., I, and XY. 
Rotalia, 
Rosalina, 
Yalvulina, 
Bulimina, ■ 
UviGERINA, 
Clavulina. 
§ The Stycostegua are divided by M. D’Orbigny into eight genera: the Nodo- 
SARiA, which he subdivides into the tine Nodosaria, such as the Nautilus 7-adicu- 
lus, L. ; — Naxtt. jxcgosus, Montag., Test. Brit., XIV. f. 4 ; and into Dentalina, 
such as the Nautilus rectus, Montag., 1, cit., XIX, f. 4, 7 (the genus Reophaga, 
Montf. I, 330) ; into Orthoerina, such as the Nadosaria clartdus, Lam., Encycl., 
pi. 466, f. 3 ; and into Mucronina. 
Frondicuaria, where comes Renidino complunalu, Blainv., Malac. 
Lingulina, 
Rime LINA, 
