32b YORKSHIRE TYPE AMMONITES Apr. 



32. AMMONITES CORNUTUS, Simpson, 

 (Plate XXXII) 



Original Description 

 " 53. A[mmonites] cornutus. [M. Simpson, 1843, p. 31.] 



[" I. Without a dorsal keel or furrow." p. 7. 

 " b. Armed with spines or distinct tubercles." p. 22.] 



" Volutions 5, exposed, rather rapidly diminishing, outer whorl 

 I the diameter ; radii annular, very prominent, slender, separated by 

 rather wide concave spaces ; two rows of blunt tubercles on the back ; 

 shell striated ; aperture circular ; diameter 2 inches. 



" This beautiful, highly characteristic, and rare species, is from the 

 lower beds of lias at Robin Hood's Bay ; it might have been associated 

 with A. maculatus, but the two prominences on the back, which suggest 

 the idea of horns, render it necessary to unite it with the armed ones. 

 It differs from that species, also, in the slenderness of the ribs, and in 

 the more rapid diminution of the whorls ; it approaches Sowerby's 

 A. Taylori." 



Additional Details 



Simpson, 1855, p. 71, instead of " shell striated " says " shell coarse 

 and cracked ; " adds at end, " On the back of a young specimen f inch 

 diameter, there are four rows of tubercles, two of which become obsolete 

 near the aperture." Simpson, 1884, pp. 105, 106, describes it as 

 " A. Taylori, Sow," and says it comes from " L.L., y [y], R. H. Bay" 

 (p. 105). Entered as A. Taylori in L.L. y (p. xx). 



Remarks 



Stages, conch, serpenticone ; periphery, i ; ornament, 5** declining 

 to 5*. 



Genus Phricodoceras, Hyatt, 1900 ; family, Liparoceratidae. 



For geological position and other remarks, see A. quadricornutus, 

 No. 33. 



Resrdt 



Phricodoceras cornutum, Simpson sp. 1843, Charmouthian, 

 armatum-jamesoni zone, Robin Hood's Bay, near Whitby. 



