AMMONITES Parkinsoni. 

 Tx\B. CCCVII. 



Spec. Char. Discoid, with numerous highly ele^ 

 vated radii ; whorls numerous, the inner ones 

 exposed ; radii slightly arched, bifid near the 

 front which is very narrow and plain. 



VotuTiONS numerous, with shghtly convex sides and 

 narrow edges : the arched radii are bent forward at 

 their outer ends, and nearly meet at an acute angle 

 upon the front, but do not pass over it : the edge pf tha 

 shell is nearly flat, in the east it is hollow in conse- 

 quence of the removal of the siphuncle ; the aperture is 

 oblong, narrowest towards the front. 



This is the Ammonite so frequently split, polished, 

 and sold at Bath : its outer surface is also often ground 

 and polished, shewing ramifying, sinuated, or simply 

 undulated edges to the septa, according to the depth to 

 which it has been worked. Misled by worked specimens, 

 that had lost the flat space in the middle of the edge, 

 I have erroneously referred this species to the Am. gi- 

 ganteus, at page 55 of Vol. I. while speaking of such 

 as are found near Keynsham, and those fine specimens 

 given me by Dr. Lettsom, all of which are flatter than, 

 even the variety a of the giganteus, and have more 

 whorls. The species before us occurs chiefly in Lyas, 

 a stratum not known to contain any silicious deposit ; 

 it is consequently never imbedded in Chert or Flint, 

 like the A. giganteus /3. 1 suspect it also may be found 



Vol. IV. 



