70 



AMMONITES Johnstonii. 



TAB. CCCCXLIX.— /^. l. 



Spec. Char. Discoid ; whorls 6 or 8 two thirds 

 exposed, with numerous, short, straight 

 costae upon the exposed parts ; front plain. 



JL HE numerous, very short, rounded, ribs or rather 

 perhaps elongated tubercles, do not reach quite across 

 the exposed parts of the whorls ; they are not to be found 

 upon two or three of the central whorls which however 

 may be distinguished from those of the last species by 

 their proportionally slow increase in size. 



Like the last, this species is only found very much com- 

 pressed and deprived of its external coats ; the pearl 

 that remains is excessively brilliant, and full of color. 

 Johnstone, Esq. has kindly lent m^ the splen- 

 did specimen here figured ; it was fortunately extracted 

 from the slaty beds of Lyas Clay, at Watchet without 

 injury. Several other Ammonites occur in the same 

 place, that probably belong to species found in other 

 parts of the Lyas range, but they are so flattened it ii 

 diflicult to recognize them. 



AMMONITES parvus. 



TAB. CCCCXLIX.— /^. 2. 



Spec. Char. Discoid ; surface marked with 

 diverging", undulating striae; inner whorls 

 exposed ; front rounded ; aperture oval. 



Four or five volutions almost wholly exposed, and but 

 gradually enlarging, constitute this little Ammonite ; 

 the striae are elevated, obtuse and numerous, they reach 

 over the front ; the aperture occupies one third of the 

 longest diameter. 



Casts of this shell composed of Pyrites have been 

 in Mr. Sowerby's Museum ever since 1806 without de- 

 composing ; they were found at the depth of 80 feet in a 

 newly sunk well at Tunbridge. 



