AMMvONITES— ZOOLOGICAL, ETC. 



145 



I have placedinit provisionally three species from the lower Cre- 

 taceous rocks {A. macilentus, Seranonis, and Consobrinus, with 

 the lobes of which I am only partially acquainted). This 

 group is therefore confined to the lowest beds of the Creta« 

 ceous formation, if the three species w^hich are cited should 

 eventually prove to have the characters of the lobes peculiar 

 to this division, 



19th Group. The Coronarit, Buch.— This group, bearing 

 the characters of the Plamdati, is only distinguished from it 

 by the presence of a tubercule or knob, at the point of junc- 

 tion of the bifurcations of the ribs or striae, which separate 

 in groups. Whorls elevated. Septa composed of lobes of 

 unequal parts, and of saddles formed of equal parts. The 

 dorsal lobe shorter than the superior lateral one ; the auxil- 

 iary lobes oblique ; the superior lateral lobe is above, and 

 the inferior lateral one below the tubercules. This group is 

 chiefly characteristic of the lowxr Oolite [A, Blagdoni, Bechei, 

 contractus, &c. 



20th Group. The Macrocephali, Buch. — ^^^Z/ analo- 

 gous in form, and in the ribs ors trise, to the sjroup of the Coron- 

 _ G!m, with this difference, that it is frequently more tumid, and 

 the turbercule, instead of being placed towards the centre of 

 the whorl, is nearer the umbihcus; hence the superior lateral 

 and inferior lobes are both above the tubercule, instead of one 

 beneath and the other above, as in the CoronariL The most 

 tumid species are peculiar to the Jurassic formation {A. Lal- 

 Herii, Brochii, Banksii), the former belong to the lower Neo- 

 comien [A, Asterianus, fascicularis, Jeannomti, otobidichus.) 



21st Group. The Fimbriati, dJOvh.— Shell discoidal; 

 spire formed of cylindric whorls, generally contiguous, without 

 being in the least enveloped, smooth or ornamented trans- 

 versely, at certain distances, with salient ribs or furrows, 

 marking the ancient position of successive mouths. Mouth 

 circular. Septa symmetrical, formed of lobes and saddles di 



VOL. I. 3L 



