AMMONITES — ZOOLOGICAL, ETC. 



141 



dens, Fittoni, Guersanti, Mosensis, Raulinianus^ Cammatteanus, 

 from the Gault^ or Lower green sand). Second division; 

 species having the tubercules even on the sides of the back 

 (A, Dufrenoyi, pretiosus, Neocomiensis, sinuosus, asperrimus, 

 from the Neocomien ; A, Michelinianus, Archiacianus, regu- 

 larise tardefurcatuSs mammillaris, from the Gault, or Lower 

 green sand). 



l€th Group. The Ornati, Buch. — Shell x^Xher tumid^ back 

 narrow, bordered with tubercules ; another range of tuber- 

 cules about the middle of the sides. Septa formed of lobes 

 and saddles, composed of unequal parts. The dorsal lobe 

 always considerably shorter than the superior lateral one. 

 All the species are from the Oxford Clay {A. Duncani^ Cul~ 

 lowiensis, Castor, Pollux), 



SPECIES WITH THE BACK MORE OR LESS SQUARE. 



1 1th Group. The Flexuosi, ^uch.— Shell provided, late- 

 rally or around the umbilicus, with a range of tubercules, 

 and also with one on each side of the back, the centre of 

 the back slightly salient. Between the two ranges of tuber- 

 cules on the sides, there are generally ribs, inflected ante- 

 riorly. Septa formed of lobes, divided into unequal parts, 

 and the saddles, divided into equal parts. The dorsal lobe 

 shorter than the superior lateral one ; the superior lateral 

 lobe very large. All the species are from the Lower Neoco- 

 mien {A. Leopoldinus, CryptoceraSy radiatus, Heliacus, Cas- 

 tellanensis.) 



1 2th Group. The Compressi, d'Orh.-— Shell generally 

 much compressed, whorls large, embracing, furnished with ribs 

 or stride on the side, all slightly curved, forming tubercules on 

 the back. Back narrow, and truncated or squared. Septa 

 composed of a large number of lobes, formed of unequal 

 parts, saddles often formed of equal parts. Dorsal lobe very 



