92 BLUE CHALK MARL. 



This species is thicker than A. lautus, and differs from it in the flat- 

 ness of the keel, and in having but two rays to each tubercle ; it may be 

 distinguished from A. auritus, by the insertion of the wreaths. 



Tab. xxii. fig. 6. A cast of indurated marl, partially covered with the 

 remains of the shell. 



20. Ammonites tuherculatus. 



Involute, umbihcate, umbihcus expanded ; volutions rounded, inner 

 whorls nearly two-tliirds exposed ; inner margin oblique, smooth, a row of 

 strong tubercles in the centre of each volution, united by obhqvie trans- 

 verse ridges to a corresponding row on the outer margin ; carene broad, 

 bordered by opposite diverging tubercles ; aperture obovate. 



A strongly marked shell, composed of three or four volutions, orna- 

 mented with remarkably prominent oblong tubercles, which, in some in- 

 stances, are 0-4 inch high ; these are placed obliquely, and united by 

 ridges that arise in pairs from the inner row. The inner volutions are 

 partly inserted, the outer row of tubercles being concealed. The middle 

 of the carene has a deep narrow sulcus or groove, and is bordered by the 

 marginal set of tubercles. The umbiUcus is in the form of a broad in- 

 verted cone. 



This species differs from the last, in the situation and size of its tubercles, 

 and in their being united by single ridges, which are not curved ; in the 

 volutions being more exposed, the carene sulcated, and the marginal tu- 

 bercles opposed to each other, instead of alternating ; this circumstance 

 also separates it from A. auritus. The septa are very foliaceous. It 

 occurs at Eingmer "*. 



Hamites. 



Fragments of the straight part of the shells of this genus, are very 

 common in every locality of the blue marl ; some of them possess a pearly 



* Mr. Parkinson describes three other species of ammonites from the blue marl of 

 Folkestone, viz. A. serratus, A. pansus, and A. ornatus. Fragments occur in this neighbour- 

 hood which, in all probability, belong to some of these ; but tpey are too imperfect to allow of 

 their characters being distinguished with certainty. 



