MOLLUSCA. 
16 
is also upon conjectures of a similar nature that reposes the classifi- 
cation of the 
Ammonites, Brug. 
Or the Cornua- Ammoni, or horns of Ammon* * * * § , for they no longer 
exist except among fossils. 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 Avheel. 
Their subdivisions are based upon the variation of their volutes and 
sijjhons. 
The name of Ammonites Lam., {Simpletjades, Montf., 82) is parti- 
cularly restricted to those species in which all the whorls are visible, 
and their siphon near the marginf. 
They have lately been divided into the Ammonites planites, of 
Haan, where the edge of the septa is foliaceous, and into the ceratites 
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 Pela- 
guses, Month, 62, in all of which the siphon is situated as in the pre- 
ceding ones. 
Tlie Scaphites Sowerb., are those in Avhich the whorls are conti- 
guous and in the same plane, the last one excepted, which is detached 
and reflexed on itself. 
Some, Bacu/ites, Lam., are entirely straight without any spiral por- 
tion whatever. 
Some of them are round ,§ and others compressed. || The last some- 
times liaA^e a lateral siphon. 
The first cells of some of them — the Hamites Sowerb., are arcuated. 
Finally, those Avhich vary most from the usual form of this family 
are the Tiirrilites, Montf., 118, where the Avhorls, so far from running 
4to, 1827 ; and that of M. J. S. Miller on the same subject in the Geol. Trans., 
second series, vol. II, part I, London, 1826. See also Sage, Journ. de Phys. an. 
IX, and Raspail, Journ. des. Sc. d’Observ., second No. To this genus we refer the 
P«cli/e Montf., 318; — the Thalamule, 322; — the AcJwlaite, 358 ; — the Cetocine, 
370 ; — the Acame, 374 ; — the Belemnite, 382 ; — the Hibolite, 386 ; — the Prorodmgue, 
390 ; — the Pirgopole, 394, which are the cases of different species. As to the 
Amimone, Id., 326 ; — the Callirhoe, 362 ; — the Chrisaore, 378, they appear to be 
mere nuclei or piles of alveoli detached from their cases. 
* So called from the resemblance of their volutes to those of a ram’s horn. 
-f- 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. I, 28, and in that of M. de Roissj', in 
Sonini’s Buft’on, Mollusca, V. 16. See also the Monograph of Haan, entitled 
“ Monogi-aphioe Ammoniteonun ef Goniateorum Specimen," Leid. 1325. 
X Sc. obliquus, Sowerb. ; Cuv., Oss. Foss., II, part II, pi. ii, f. 13. 
§ liaculites vertebralis, Montf. 342 ; Fauj., Mont, de St. Pierre, pi. xxi. 
II The Timnitc, Montf., 346; W.alch., Petrif., Supp., pi. xii, constitutes the 
genus Rhabdites of Haan, who refers the Icthyosarcolites of Desmar to it. 
