66b YORKSHIRE TYPE AMMONITES Oct. 



66. AMMONITES SIMPSOXI, Bean-Simpson 

 (Plates LXVIa, B) 



Original Description 

 " 68. A[iniOMTEs] SiMPSoxi, Bean's MSS. [M. Simpson, 1843, pp. 37, 38.] 



[" II. With a keel on the back. 

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



" Very much depressed ; volutions 4 or 5, inner ones J concealed, 

 outer whorl \ the diameter, sides undulating, inner margin rounded ; 

 radii nearly obsolete on the outer whorl, bend towards the aperture ; 

 striae [p. 38] diverging, numerous, and delicate ; keel sharp, prominent ; 

 apertm-e acutely triangular ; diameter 6 inches. 



" This ammonite, which Mr. Bean has been pleased to call 

 A. Simpsoni, is from the lower has shale at Robin Hood's Bay ; the whorls 

 swell out in thickness towards the inner margin, which is finely rounded, 

 whilst the part near the keel is shghtly concave ; in the older specimens 

 the radii are scarcely discernible. 



Additional Details 



Simpson, 1855, 79, omits "very" at beginning; 1884, 115, adds 

 at end of ist par. " L.L., 15, R. H. Bay." 



Remarks 



Stages, conch, oxycone ; jjeriphery, 2c ; ornament, ic. The radial 

 curve can just be followed in places : on the side it is straight, on the 

 periphery much projected. 



The f>eriphery is very sharp ; on each side of it is a somewhat broad 

 depressed area, so that the exterior is acutely conca\'ifastigate. Inside 

 the depressed area the whorls become gibbous, with greatest thickness 

 about ith from inner margin. The whorl-section is thus acutely galeati- 

 form. The umbilical edge is steeply rounded, but not defined. 



The sf)ecimen has suffered from crushing on one side. 



The suture-Hnes are not clearly exposed. The type shows only one 

 prominent accessory lobe in the external saddle. A tof)otype about 

 190 mm. diameter (Jermyn Street Museum, Xo. 24,362), just commencing 

 body chamber, shows at 166 mm. diameter two such lobes. 



The galeatiform whorl-section, the somewhat simple suture-line 

 and the loss of ornament while the umbilicus is, for an oxycone, com- 

 paratively of)en, suggest that this species is a degenerate development 

 of Am. colesi, J. Buckman, and Am. scipionianus, d'Orbigny, and is not 

 an Oxynoticeras. 



Genus, Aetomoceras, H5ratt, (Gen. vii) ', family Arietidae, Hyatt. 



Result 



Aetomoceras simpsoni, Be.\n-Simpson sp. 1843, Sinemurian, 

 oxynotum zone, Robin Hood's Bay, near Whitby. 



