7 ob YORKSHIRE TYPE AMMONITES-II May 



70. AMMONITES GUBERNATOR, Bean-Simpson 

 (Plate LXX) 



Original Description 

 " 27. A[mmonites] gubernator, Bean's MSS. [M. Simpson, 1843, 

 pp. 17, 18.] 



["I. Without a dorsal keel or furrow. 

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



" Depressed ; volutions 4 or 5, inner ones J concealed, outer whorl 

 not quite \ the diameter, inner margin prominent, suddenly rounded ; 

 aperture ovate ; diameter 3 inches. 



" This is a smooth, bright shell, without radii or striae. In the rapid 

 diminution of the whorls it resembles A. fimbriatus, but the [p. 18] 

 prominence of the inner margin of the whorls, and the partial concealment 

 of the inner ones, at once distinguish it." 



Additional Details 

 Simpson, 1855, p. 40, omits " depressed " ; 1884, 68, describes it 

 as " A. jurensis, Zeit. Pal. lxxiv., f. 3 " [Wright's Mon. Lias AmmJ ; 

 adds " U.L., 1, Peak." 



Remarks 



Proportions, 79, 41, 34, 31 : Platy-, pachygyral, sublatum- 

 bilicate. 



Stages, conch, serpenticone ; periphery, 1 ; ornament, ic. 



There are signs of a corrugate stage in the inner whorls (S. Buckman, 

 1905, p. 143), and the umbilical edge (shoulder) is steep and prominent. 

 The whorl is subtriangular, and the greatest thickness near the margin. 



Genus, Pleurolytoceras, Hyatt, 1900, p. 572 ; S. Buckman, 1905, 

 p. 143 ; family Lytoceratidae. The species is possibly a smooth cata- 

 genetic development of the hircinum group. If it is not, it requires 

 a new generic name, for the umbilical edge is too pronounced and steep 

 for Alocolytoceras. 



Geological position, striatulus shales is the horizon suggested by the 

 little matrix remaining. Lyt. quenstedti is from striatulum zone (Brasil). 

 A. perlaevis is found in the dispansum zone of Gloucestershire and 

 Yorkshire. 



Result 

 Pleurolytoceras gubernator, Bean-Simpson sp. 1843, Yeovilian 

 [striatulum zone], Peak, S. of Robin Hood's Bay, near Whitby. 



