18 MOLLUSCA. 



M. D'Orbigny, who has exceeded every 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. 



When the cells are simple and spirally arranged, they constitute 

 his Heficostegua, AA'hich are again s\ibdivided. If the whorls are en- 

 veloped, as is particularly the case in the Nummulites, they become 

 his Helicostegua nautUoida*. 



If tlie whorls do not envelope each other, they are the Helicostegua 

 amrnonoida.] 



If the whorls are elevated as in most Univalves, they are the 

 Helicostegua turhinoida.\ 



Simple pells may also be strung upon a single, straight or slightly 

 curved axis, constituting the family of the Stycoslegua.% 



* 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 Nummulines, — 

 Nautilus iiompiloides, Ficht., and Moll., N. incrassatus, Id. 

 The Syderglii^a, the same as Syderolites, Lam. 



Cristellaria, — Nautilus cassis, Naut. galea, Id., &c. 



RoBULiNA, Nautilus calcar, Naut. voHex, Id. 



Spirolina, — Spirdlinites cylindracea. Lam. Anim., sans verteb, 



Peneropla, — Nautilus planatus, Ficht. and Moll., &c. 



Dentritina, 



polystomella, 



Axomalina, 



Vertebralina, 



Cassidulina. 

 t M. D'Orbigny divides them into four genera : 



soldania, 



Operculina, 



Planorbulina, 



Planulina. 

 X These form ten genera : 



Truncatulina, 



Gyroidina, 



Globigerina, 



Calcarina, -where is placed, among otbei*s, the Nmtiius Spenykri, Fich. and 

 MoU. XIV, d., I, and XV. 



ROTALIA, 



e.osalina, 



Valvulina, 



bulimina, 



uvigerina, 



Clavulina. 

 § The Stycostegua are divided by M. D'Orbigny into eight genera : the Nodo- 

 SARiA, which he subdivides into the true Nodosaria, such as the Nautilus radicu- 

 lus, L. ; — Naut. juyosus, Montag., Test. Brit., XIV. f. 4 ; and into Dentalina., 

 such as the Nautilus rectus, Montag., I, cit., XIX, f. 4, 7 (the genus Reophaga, 

 Montf. I, 330) ; into Orthoerina, such as the Nadosaria clavulus, Lam., Encjcl., 

 pi. 466, f. 3 ; and into Mucronixa. 



Frokdicuaria, where comes Rcnulino complamda, Blaiiiv., Malac. 



LiNGULINA, 

 RiMXJLINA, 



