35b YORKSHIRE TYPE AMMONITES Apr. 



35. AMMONITES RADIATUS, Simpson 

 (Plate XXXV) 



Original Description 

 " 89. A[mmonites] radiatus. [M. Simpson, 1843, p. 47.] 



L"II. With a keel on the back." p. 31. 

 " b. Outer whorl narrower." p. 44] 



" Volutions 4, inner ones \ concealed, outer whorl not quite \ the 

 diameter, sides rounded ; radii straight, numerous, sharp, regular, delicate, 

 nearly obsolete on the rounded back where they turn towards the ajierture ; 

 keel slender, rather rounded, furrow on either side slight ; aperture ovate ; 

 diameter i inch. 



" This is an exceedingly beautiful and well-defined species ; the radii 

 are all as if drawn with geometrical exactness ; the keel and all its parts 

 have the greatest regularity. I have seen 5 or 6, all small and uniform, 

 and entirely unlike the young of A. geometricus, Bucklandi, or any other 

 species ; it occurs in the lower lias at Robin Hood's Bay." 



Additional Details 



Simpson, 1855, \)\>. 88, 89.— p. 89, after " dehcate " in first ]mr. 

 " bend towards the aperture near the back ; the keel slender, rather 

 roinided, furrows distinct ; aperture ovate ; diameter | incli." In second 

 par. after " exactness ; " " those near the ai)erture slightly waving, 

 absent in the centre ; the keel — ." Simpson, 1884, \>. 126, as 1855. 



Remarks 



Stages, conch, becoming oxycone ; periphery, 4 ; ornament, 4c. 

 The specimen, figured X2, is quite a young form. 



Genus, Arietites, Waagen, 1869 ((ien. vi) ; family, Arietidas, 

 Hyatt. Geological position about L.L. lO, presumably. 



Result 



Arietites kadiatus, Simpson sp. 1843, Sinemuriau, [stellare zone], 

 Robin Hood's Bay, near Whitby. 



