108 
blended, the turns being apparent on both sides, and the siphuncle 
obvious ; but which have been generally considered as recent Cornua 
ammonis. 
It is true that Lamarck says : “ Les discorbes seroient de veritable 
nautiles, si leur tours de spire, au lieu d’etre tous entierement appa- 
rens et a decouverts, etoient caches par la dernier tour enveloppant 
les autres ou les recouvrant par sa paroi exterieure, et si elles ne 
manquoient de syphon. Si ces memes coquilles ayant leur tours de 
spires h decouvert et bien apparens, avoient leur cloisons perforees 
par un syphon, elles seroient alors des spirolines*.” But on referring 
to the genus Spirolina, this genus is found to have been formed for 
the reception of those minute shells, which, being partly spiral and 
partly straight, differ from those of the genus Spirula, only in having 
their spiral turns contiguous. 
It therefore seems necessary to make a still farther separation, and 
to dispose of these shells, in which the characters of Nautilus and 
Ammonites are blended, under a distinct genus. This is the more 
requisite, since thus the error would be more plainly shown of consi- 
dering these shells as ammonites, of which genus none have been yet 
found in a recent state. The characters of such genus— a discoidal, 
multilocular spiral univalve, with all the turns visible on both sides, 
and the septa pierced with an obvious siphuncle— seem to me suffi- 
ciently strong and distinct to authorize the formation of a separate 
genus, which might be marked by the term Ammonautilus, expressive 
of its mingled characters. 
I shall not, however, presume on such a change ; but having made 
these suggestions, will leave them under the genus Nautilus. 
N. JBeccarii, Linn. Plane. Conch, min. not. Tab. i. Fig. 1, claims 
the first notice, in consequence of its being the first discovered shell 
of this family, and that which gave rise to the supposition of the ex- 
istence of recent Cornua ammonis. 
* Annales de Mus. d’Hist. Nat. Tome V. p. 182. 
