AMMONITES. — ZOOLOGICAL, ETC. 



321 



A, Ligatus, A. Seranonis. 



Matheroni. Strangularis, 



Ophiurus. Striatisulcatus. 



Quadrisulcatus, Subfasicularis. 



Raresulcatus. Subfrimbriatus. 



Royerianus. Tortisulcatus, 



Semisulcatus, Terverii. 

 We find this character especially marked in the Neo- 

 comien, whilst it scarcely exists in the Jurassic formation. 

 In the gault it is only observed in four species, A. Mayoria- 

 muSj latidorsatus, Parandieri and Dupiniamus ; thus we may 

 state that the most predominant exterior form and most 

 peculiar to the Neocomien, is that of having these marks of 

 a cessation of growth, 



2nd. Amongst the exceedingly various and diversified 

 forms of the Ammonites of the gault, or lower green sand^ 

 where the external ornaments are very prominent, we re- 

 mark one character which is more general than all the rest ; 

 which is the presence, on each side of the back, of a range 

 of salient portions more or less tubercular, formed by the 

 ribs, which, being alternate or in pairs, are interrupted at 

 that place. We observe this character in twenty- seven Am- 

 monites out of forty-two, being more than one half of the 

 whole number. 



Archiacianus. 



A. Itierianus. 



Auritus. 



Interriiptus, 



Brottianus. 



Lautus. 



Camatteanus. 



Mammilaris. 



Cristatus. 



Michelinianus. 



Delarnei. 



Milletianus. 



Denarius, 



Mosensis, 



Fittoni, 



Nodosocostaius. 



Guersanti. 



Puzosianus. 



Hugiardianus, 



Quercifolius > 



Inflatus, 



Rauliniams, 



