4ob YORKSHIRE TYPE AMMONITES Nov. 



40. AMMONITES ACUTICARINATUS, Simpson 

 (Plate XL) 



Original Description 

 " 171. A[mmonites] acuticarinatu;;. [M. Simpson, 1855, p. 94.] 

 [" III. Keel between two furrows." p. go. 

 " b. Furrows distinct." p. gj.] 



" Volutions 7 or 8, exposed ; radii separated by concave spaces, 

 sharp, faint on the inner margin, gradually increasing towards the keel, 

 where they suddenly turn towards the mouth ; keel slender, sharp, 

 prominent, entire ; aperture ovate ; diameter 2-} inches. 



" This greatly resembles A. semicostatus, but the sides of the whorls 

 are more rounded, the keel sharper and more prominent, and without 

 any distinct furrow on either side. It is from the Lower Lias at 

 R. H. Bay. 



" I formerly named this shell A. Youngi ; but I was afterwards 

 reminded that another from the Speton clay (A. rotula, Sow.) had been 

 named A. Youngi, by Mr. Bean, and described by Young, previous to 

 the publication of Sowerby's description." 



Additional Details. 



Simpson, 1884, 133, 134, adds " L.L., 25, R. H. Bay " to end of 

 first paragraph. Omits last sentence of the second. 



Remarks 

 Stages, conch, serpenticone ; periphery, 4 ; ornament, 1-5. 

 Genus, Arnioceras, Hyatt, 1867 (Gen. vl) ', family Arietidae. 



Result 

 Arnioceras acuticarinatum, Simpson sp. 1855, Sinemurian, [semi- 

 costatum zone], Robin Hood's Bay, near Whitby. 



