81) YORKSHIRE TYPE AMMONITES Dec. 



8. AMMONITES POLYOPHYLLUS, Simpson 

 (Plate VIII) 



Original Description 

 " 71. A[mmonite.s] polyophyllus. [M. Simpson, 1843, p. 39.] 



[" II. With a keel on the back. 

 "a. Outer whorl broad." p. 31.] 



" Much depressed ; volutions 5, inner ones very little exposed, outer 

 whorl i the diameter, inner margin rounded, sides convex, then concave ; 

 back thin ; radii obtuse, depressed, waving ; keel sharp, much elevated ; 

 aperture triangular ; diameter 3I inches. 



" This Ammonite is distinguished by the great number and regularity 

 of the foliations of the septa, which ornament the whole surface of the 

 whorls by their meanderings ; the inner edge of the whorls are rounded, 

 as in A. Simpsoni, and the thin back is greatly produced, so as to be 

 easily knocked off. The radii, in general, are nearly obsolete towards 

 the inner margin of the whorl, and become gradually more distinct towards 

 the back, but a fine specimen in the possession of Mr. Bean is entirely 

 destitute of radii." 



Additional Details 

 Simpson, 1855, p. 81, "A. polyphyllus," with same description; 1884, 

 p. 117, omits a Httle, but adds " L.L., R. H. Bay [Lower Lias, Robin 

 Hood's Bay]." 



Remarks 



Stages, conch, oxycone ; periphery, 2c ; ornament, 3c. 



The species belongs, at present, to the genus Oxynoticeras, Hyatt 

 (Gen 77), and family Arietidse. It presumably came from the 

 indurated band, Div. 13, (Simpson, 1884, p. xxi). 



Result 



Oxynoticeras polyophyllum, Simpson sp. 1843, Sinemurian, 

 [oxynotimt-zone,] Robin Hood's Bay, near Whitby. 



