318 MOLLUSCA. 



If the whorls do not envelope each other, they are the Helicos- 



TEGA AmMONOIDA(I). 



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



LICOSTEGA TuRBIN0IDA(2). 



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

 curved axis, constituting the family of the Styoostega(3). 



Or they may be arranged in two alternate series, when they be- 

 come the Enallostega(4). 



Vertebralina, 

 Cassidulina. 

 { 1) M. D'Orbigny divides them into four genera: 

 soidania, 

 Opehculina, 



PlANORBULINA, 

 PlANUIINA. 



(2) These form ten genera: 



TttUNCATULINA, 



Gtroidina, 



GLOBlGERIIfA, 



Calcarina, where is placed, among others, the Nautilus Spengkri, Fich. 

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



ROTALIA, 



rosalina, 



Valvulina, 



bueimina, 



uvigerina, 



Clavulina. 



(3) The Stycostega are divided by M. D'Orbigny into eight genera: the Nodo- 

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

 lus, h.iNaut.jugosus, Montag., Test. lirit.,XlV, f. 4; and into Dentaiina, such 

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

 I, 330); into Orthocerika, such as the Nodosaria c/aro/us, Lam., EncycL, pi. 466, 

 f. 3; and into Mucronina. 



Frondicularia, where comes Renulina complanata, Blainv., Make. 



LlNGUtlNA, 

 RlMULINA, 



Vaginulina, to wlilch belongs the Nautilus legumen, Gm., Plane, I, f. 7; En- 

 cy., pi. 465, f. o. 



Marginulina, where we find the Nautilus raphanus, Gm., Soldan., II, xciv. 

 Peanularia, such as the Nautilus crepidulus, Fich., and Moll., XIX, g, h, i. 

 Pavonina. 



(4) M. D'Orbigny has five genera of Enallostegac: 



BlGENERIJfA, 



Textularia, 

 vulvulina, 



DiMORPHINA, 

 POLTMOBPHINA, 



