67b YORKSHIRE TYPE AMMONITES Oct. 



67. AMMONITES DENOTATUS, Simpson 

 (Plates LXVII A, b) 



Original Description 

 " 122. A[mmonites] denotatus. [M. Simpson, 1855, p. 76.] 



["II. With a keel on the back. 

 " a. Outer whorl broad." p. 72.] 



" Volutions 5 or 6, inner whorls J concealed, outer whorl less than 

 \ the diameter, inner margin rounded, outer part depressed ; radii straight 

 for about | the width of the whorl, then suddenly bend towards the 

 aperture, where they become obsolete, terminate abruptly at a flattish 

 groove, which relieves the sides of the whorl from the keel ; which is 

 prominent, sharp, entire ; aperture ovate ; diameter 6 in. — L.L.; Mr. 

 Leckenby's Col." 



Additional Details 



Simpson, 1884, iii, adds after name " Simp. Pal. pi. vi., f. i. 

 [Wright, Mon. Lias Amm. ; Pal. Soc. 1878]. 



Remarks 



Stages, conch, oxycone ; periphery, 4c ; ornament, 4c, rapidly 

 failing. 



Genus, Arietites, Waagen (Gen. vi) ', family, Arietidae. Geological 

 position, — Blake, 1876, 290 (Ar. collenoti), says " middle portion of 

 oxynotus zone," which he uses in a wide sense = obtusuni-raricostatum 

 zones. Therefore about Simpson's L.L. 16 may be the bed. 



The type passed with the Leckenby collection to the Woodwardian 

 (now Sedgwick) Museum, Cambridge, and was kindly lent by Prof. Hughes 

 for this work. It was figured by Wright, 1881, xxii b, as Arietites 

 Collenotiii, but with ribs depicted far too strong. He gives the locahty 

 as Robin Hood's Bay (1881, p. 306). 



The differences between this species and A. fowleri, J. Buckman, 

 1844, are not great : the present species has a slightly smaller umbilicus 

 and rather stronger, rather more distant ribs. The difference of ribbing 

 may be partly a matter of age : the two types are of different sizes and 

 not easily compared. 



The present type possesses only the outer whorl and three parts 

 of the ne.xt : the rest of the umbihcus is wanting — it has been made up 

 and scored with the chisel. 



Result 



Arietites denotatus, Simpson sp. 1855, Sinemurian, [stellare zonel, 

 Robin Hood's Bay. 



