39b YORKSHIRE TYPE AMMONITES Nov. 



39. AMMONITES SCORESBYI, Simpson 

 (Plates XXXIXa,b,c) 



Original Description 



" 14. A[mmonites] Scoresbyi. [M. Simpson, 1843, p. 12.] 



[" I. Without a dorsal keel or furrow. 



" a. No spines." p. 7.] 



" Volutions 6 or 7, exposed ; radii prominent on the sides, obsolete 

 on the back and on the inner margin of the whorls, nearly equal to the 

 concave spaces between them ; striae annular, fringed ; aperture circular ; 

 diameter 8 inches. 



" In many respects this resembles A. Belcheri ; but the fimbriated 

 stria;, the form of the aperture, as well as its large size, and coarse radii, 

 point it out as a distinct species. On the sides of the whorls, also, may 

 be traced two rows of obscure tubercles. All that I have seen were of 

 a large size, and were procured from the lowest beds of Lias at R. H. Bay. 

 I have named it in honour of the Rev. Dr. Scoresby, a native of Whitby, 

 who has done eminent service to Natural History, and Physical Science ; 

 and who, from comparatively small beginnings, by close application, 

 activity, and perseverance, has raised himself to successive stations of 

 honour and usefulness." 



Additional Details 



Simpson, 1855, 69, places the species under " b. Armed with spines 

 or distinct tubercles " [p. 58] — " Two rows of spines " [p. 68]. He adds 

 [p. 69], after " sides," " with two rows of blunt tubercles " ; after " striae," 

 has " obsolete " ; instead of 2nd par., has " This is principally dis- 

 tinguished from A. Birchii by the smallness of the tubercles. — L. L., 

 R. H. Bay." 



Simpson, 1884, 103, as 1855. 



Remarks 



Stages, conch, scrpenticone ; periphery, i ; ornament, 5**, with 

 signs of catagenesis to a costatc stage. 



This is the bituberculate species of the genus. By " striae fringed " 

 Simpson means the condition of test illustrated by .Wright, 1880, xxv, 2, 3. 



Genus, Xipheroceras (Gen. iv) ; family Deroceratidae, Hyatt. The 

 geological position is presumably about L.L. 21-23. 



An immature example from the Lycett coll. labelled " L.L., R. H. 

 Bay " is preserved in the Geological Survey Museum, No. 23616, and is 

 depicted PI. XXXIX C. Its ontogeny shows ornament i, 3, 4, 5*, 5**, 

 or the passage from a planicosta through a ziphus stage to scoresbyi. 

 Stage 5** is first perceptible at about 12 mm. diameter. 



Result 

 Xipheroceras scoresbyi, Simpson sp. 1843, Sinemurian, [obtusum 

 zone] Robin Hood's Bay, near Whitby. 



