165 

 Ammonites, Bruguwre, 1792. 



CoRNU Ammonis, Lister, Lang, and other old authors. 



Ammonites, Planulites, Okbulites, Lamarck. 



Orbulites, Ammonites, de Blainville. 



Planulites, Ellipsolites, Amaltheus, Pelaguse, Symplegade, Mont. 



Ammonites, Ellipsolites, Sowerhy. 



Nautilus, Argonauta, Eeinecke. 



Ammonites, Planulites, Globites, Ceratites, De Haan. 



Animal unknown ; shell multilocular, spiral, discoidal, compressed, or 

 ventricosej whorls regularly convoluted on the same plane, alv^ays 

 conticnioas, and more or less involute ; chambers separated by transvei^e 

 septa! flat or convex in the middle, and deeply sinuated at the 

 outer border, forming on the mould, beneath the shell, a very complicated 

 arrangement of brandling sutural lines; siphuncle external, dorsal as 

 regards the shell ; dwelling chamber large, sometimes exceeding an entire 

 yrhovl; mouth variously formed, often contracted, and compressed, eUip- 

 tical, oblong, rounded,quadrate,orventricose, according to the shapeof the 



shell; aperture furnished with thickened bands, or lateral processes of 

 various forms and dimensions in the different species. 



The marginal foliation of the septa was supposed by VON BucH, who 

 first described them in detail, to afford a permanent character for the 

 diagnosis of the species; to facilitate their description he called the 

 outlines of the septa sutures; when they are folded the elevations are 

 saddles, and the intervening depressions lobes, which form the more 

 subdivided and branched portion of the edges of the septa, and extend 

 backwards from the aperture; the saddles are less subdivided, their 

 folioles more rounded, and they project foi-ward towards the mouth. 



The lobes are divided into dorsal, superior and inferior lateral, 

 auxiliary, and ventral. 



The dorsal lobe is single, surrounds the siphuncle, and occupies tlie 

 middle region of the back of the shell. The superior lateral lobe is in 

 general large, and situated at the upper third of each side of the whorl. 



The inferior lateral lobe is smaller than the superior latei-al, and is 

 seen on the lower third of the whorl ; the auxiliary lobes, two or 

 three in number, are disposed obliquely near the inner margin, and 

 the single ventral lobe is situated in the middle region of the whorl, 

 opposite the dorsal lobe, and resting^upon the previous turn of the shell. 

 The saddle are subcUvided into the dorsal saddle, situated between 

 the dorsal and the superior latei-al lobes; the lateral saddle, hctween the 

 superior lateral and inferior lateral lobes; and the auxiliary saddles, 

 between the auxiliary lol^s. 



