33b YORKSHIRE TYPE AMMONITES Apr. 



33. AMMONITES QUADRICORNUTUS, Simpson 

 (Plate XXXIII) 



Original Description 

 " 109. A[mmonites] quadricornutus. [M. Simpson, 1855, p.71.] 



[" I. Without a dorsal keel or furrow." p. 35. 



" b. Armed with spines or distinct tubercles." p. 58. 

 " Two rows of spines." p. 68.] 



" Volutions 4 or 5, exposed, outer whorl more than J the diameter ; 

 radii aunular, very prominent, rounded, slender, separated by wide 

 concave spaces, armed with four rows of strong blunt spines on the 

 back ; shell thick, striated transversly ; aperture round ; diameter 

 2 inches. 



" Whether it is possible that this can be merely a variety of the 

 last [A. cornutus] or not, I would not take upon me to say. The whorls 

 are less inflated, the ribs more prominent, and the spines in general 

 strongly developed, especially those on the middle of the back ; and 

 I believe it is from a different bed ; but one of the radii, I observe, is in 

 every respect like those of A. cornutus. If it is not a distinct species, 

 it is certainly a very interesting variety, and worthy of a separate 

 description. — L.L. ; R. H. Bay. Mr. Morley's Col." 



Additional Details 



Simpson, 1884, p. 106, reads " annular " and " transversely " ; 

 for " A. cornutus " has " A. Taylori " ; adds at end, " Whitby Museum." 



Remarks 



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

 5***, for there is swelling on umbilical border. 



This species is much nearer to A. taylori, J. de C. Sowerby, than is 

 A. cornutus ; but its whorls are less tumid and its ribs, in inner whorls, 

 more approximate. 



This species and A. taylori represent a stage of development which 

 A. cornutus has passed through. Genus, Phricodoceras, Hyatt, 1900 ; 

 family, Liparoceratidae. The geological position is probably much the 

 same as that of A. cornutus; but this shows a clayey matrix, while 

 A. cornutus is pyritized. A. cornutus, therefore, probably occurs in the 

 pyritous band at top of Simpson's L.L. y. (p. xx), and A. quadricornutus 

 in the shale below. 



Result 



Phricodoceras quadricornutum, Simpson sp. 1855, Charmouthian, 

 [annatum-jamesoni zone], near Whitby. 



