70 
AMMONITES Johnstonii. 
TAB. CCCCXhlX.— Jig. 1. 
Spec. Char. Discoid ; whorls 6 or 8 two thirds 
exposed, with numerous, short, straight 
costae upon the exposed parts ; front plain. 
The 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 me 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 speeie9 found in other 
parts of the Lyas range, but they are so flattened it is 
difficult to recognize them. 
AMMONITES parvus. 
TAB. CCCCXL1X — fig. 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. 
