AMMONITES — ZOOLOGICAL, ETC. 



U9 



Mouth ? Septa divided into a great number of lobes, formed 

 of unequal parts ; the saddles formed of equal or almost 

 equal parts. Dorsal lobe, shorter than the superior lateral 

 lobe. The saddles and lobes wide and short. The species 

 belonging to this group are found in the Cretaceous rocks ; 

 A, clypeiformis^ Georilianus, Nisus, difficilis^ from the lower 

 Neocomien ; bicurvatus, from the Gault ; Requienianus and 

 Goupilianus, from the Chloritic chalk, or Upper green sand). 



SPECIES HAVING A SALIENT BACK, CRENULATED ON 

 THE MESIAL LINE. 



6th Group. The Amalthei, Buch. — Shell provided, on 

 the sides, with very slight ribs, inflected anteriorly, the back 

 sharp, divided into salient, transverse folds, causing a crenu- 

 lated surface. Mouth provided, anteriorly, with a beak, on 

 the mesial line, of which the crenulations are the ancient 

 traces. Septa formed of lobes and saddles, divided into une- 

 qual parts. Dorsal lobe shorter than the superior lateral 

 lobe. All the species belong to the Jurassic, or Oolite For- 

 mations {A. Amaltheus, cordatus, sery-atus, ^c.) 



7th Group. The Pulchelli, d'Orb. — Shell equally di- 

 vided, on the sides, by straight, salient ribs, having no inflec- 

 tion, which pass from side to side, leaving, on the back, a 

 compressed tubercle, representing a series of crests. Mouth ? 

 Septa formed of lobes, divided into unequal parts, and of 

 saddles, divided into equal parts. Dorsal lobe nearly equal 

 in length to the inferior lateral lobe. All the species are 

 from the lower Cretaceous rocks [A, PulchelluSy from the 

 Neocomien ; A. Brottianus and Itieranus, from the Gault, or 

 Lower green sand). 



8th Group. The Rhotomagenses, d'Orb. — Shell with the 

 whorls turned, square or oval, ornamented with salient ribs, 

 more or less supplied with tubercles, in four or five lines, one 



