78b YORKSHIRE TYPE AMMONITES— II August 



78. AMMONITES GAGATEUS, Young & Bird 

 (Plate LXXVIII) 



Original Description 

 [Young & Bird, 1828, pp. 255, 359.] 



" No. 7 [Plate XII] is a rare and beautiful little ammonite from the 

 hard bands in the alum shale of the Hawsker shore. It is a smooth 

 shining black shell, with very prominent ribs, each of which passes over 

 the back undivided, and unaltered, or very slightly flattened. The 

 aperture is round, or, rather, transversely oblong, the whirls being 

 narrower on the sides than on the back ; and they diminish very regularly, 

 the smaller whirls showing their prominent ribs like rows of jet beads. 

 We may name this shell A. gagateus. 



" [P- 359] Plate XII. fig. 7. A. gagateus. Lias bands." 



Remarks 



Proportions, 47, 22, 30, 54 ; substeno-, subpachygyral, sub- 

 extremilatumbilicate. 



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



In a strong light, at a certain angle, may be seen a slight indication 

 of a median keel on the periphery : the ribs cross it at right angles. 



This is a polygyral species, with numerous inner whorls, whereon 

 the ribs are prominent and distant — characters which they retain on 

 later whorls. 



The suture-line is simple, and feebly denticulate : the lobes are 

 short and broad, the ES wide and shallow. 



Genus, Gagaticeras, nov. (II, v) ; family Echioceratidse, nov. (II, v), 

 or Liparoceratidae. 



Geological position, Blake, 1876, 276, says " zone of A. oxynotus " ; 

 Simpson, 1884, 75, gives "L.L. 13, R.H. Bay " ; p. xxi, places it in L.L. 2 

 and 13. Neither author mentions Hawsker, so that Young & Bird's 

 locality and horizon may be deemed incorrect ; so perhaps is L.L. 2, 

 unless it be a case of derivation. 



Result 

 Gagaticeras gagateum, Young & Bird sp. 1828, Sinemurian, 

 oxynotum zone, near Whitby. 



