18 MOLLU8CA. 



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 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 turbinoida.% 



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

 curved axis, constituting the family of the StycosteguaJ 



* 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 pompiloides, Ficht., and Moll., N. incrassatus, Id. 

 The SYDEROLINA, the same as Syderolites, Lam. 



CRISTELLARIA, Nautilus cassis, Naut. galea, Id., &c. 



ROBULINA, Nautilus calcar, Naut. vortex, Id. 



SPIROLINA, Spirolinites cylindracea, Lam. Anim., sans verteb. 



PENEROPLA, Nautilus planatus, Ficht. and Moll., &c. 



DENTRITINA, 



POLYSTOMELLA, 



ANOMALINA, 



VERTEBRALINA, 



CASSIDULINA. 

 t" 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 Nautilus Spengleri, Fich. aud 

 Moll. XIV, d., I, and XV. 



ROTALIA, 

 ROSALINA, 

 'VALVULINA, 

 BULIMINA, 

 UVIGERINA, 



CLAVUHNA. 



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. ; Naul.jugosus, Montag., Test. Brit., XIV. f. 4 ; and into DENTALINA, 

 such as the Nautilus rectos, Montag., I, cit., XIX, f. 4, 7 (the genus REOPHAGA, 

 Montf. I, 330) ; into ORTHOERINA, such as the Nadosaria clavulus, Lam., Encycl., 

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



FRONDICUARIA, where comes Renulino complanafa, Blainv., Malac. 



LlNGULINA, 

 RlMULINA, 



