CEIMIALOPODA. 315 



M. de Blainville divides them according to the greater or less 

 depth to which the internal cone or chambered portion penetrates, 

 or as the edges of the external cone have a small fissure or not, or as 

 the external surface is marked on one side by a longitudinal furrow, 

 or by two or more furrows towards the summit, or finally as that 

 surface is smooth and without furrows. 



Bodies very similar to Belemnites, but without a cavity and with 

 a rather prominent base, form the genus Actinocamax of Miller. It 

 is also upon conjectures of a similar nature that reposes the classi- 

 fication of the 



AMMONITES; Brug. 



Or theCornua-Ammoni(l), for they no longer exist except among fos- 

 sils. They are distinguished from the Nautili by their septa, which, 

 instead of being plane or simply concave, are angular and sometimes 

 undulated, but most frequently slashed on the edge like the leaf of 

 an acanthus. The smallness of their last cell seems to indicate that 

 like the Spirula they were internal shells. They are very abundant 

 in the strata of secondary mountains, where they are found varying 

 from the size of a lentil to that of a coach wheel. Their subdivi- 

 sions are based upon the variation of their volutes and siphons. 



The name of Ammonites, Lam., (Simplegades, Montf., 82) is par- 

 ticularly restricted to those species in which all the whorls are visi- 

 ble. Their siphon is near the margin(2). 



They have lately been divided into the Ammonites, Planites of 

 Haan, where the edge of the septa is foliaceous, and into the Cera- 

 TiTES of Haan, where it is simply angular and undulated. 



Those in which the last whorl envelopes all the others form the 

 Orbitulites, Lam., or the Globites, and Goniatites of Haan, or 

 the Pelaguses, Montf., 62, in all of which the siphon is situated as 

 in the preceding ones. 



Kaspail, Journ. des Sc. d'Observ., second No. To this g-enus we refer the Paclite 

 Montf., I, 318;~the Thalamuk,322;—the^cyioYte,35S;—ihe Cetocine, 370;— the 

 Jtcame, 374; — the Belemnite, 382; — the Hibolife, 386; — the Prorodrague,o90\ — the 

 Pirgopole, 394, which are the cases of different species. As to the Amimone, Id., 

 326; — the Callirlioe, 362; — the Chrisaore, 378, they appear to be mere nuclei or 

 piles of alveoli detached from their cases. 



(1) From this resemblance of their volutes to those of a ram's horn. 



(2) The various species of Ammonites have long been collected and described, 

 but with less care than those of other shells. We may commence studying them 

 in the article Ammonite, Ency. Method. Vers., 1, 28, and in that of M. de Koissy, 

 in Sonini's Buffon, Mollusca, V, 16. See also the Monograph of Haan, entitled 

 " Monographise jimmoniteorum et Goniafeorum Specimen,'" I.eid., 1325. 



