108 



which the characters of Nautilus and Ammonites are 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 apparens 

 et a decouverts, etoient caches par la dernier tour enveloppant les 

 autres ou les recouvrant par sa paroi exterieure, et si elles ne man- 

 quoient de syphon. Si ces memes coquilles ayant leur tours de spires a 

 decouvert et bien apparens, avoient leur cloisons perfbrees par un sy- 

 phon, elles seroient alors des spirolines *, " But on referring to the 

 genus Spirolina, this genus is found to have been formed for the recep- 

 tion of those minute shells, which, being partly spiral and partly 

 straight, differ from those of the genus Spinda, 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 Ammo- 

 nites are blended, under a distinct genus. This is the more requisite, 

 since thus the error would be more plainly shown of considering 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, arid the septa 

 pierced with an obvious siphuncle seem to me sufficiently strong and 

 distinct to authorize the formation of a separate genus, which might be 

 marked by the term Ammonautilus t 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. Beccarii, Linn. Plane. Conch, min. not. Tab. I. Fig. i, 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 existence of 

 recent Cornua ammonis. 



* Annales de Mus. d'Hist. Nat, Tome V. p. 182. 



