148 



M.K. HOWARTH 



two Apoderoceras subtriangulare (Young & Bird) (PI. 5, fig. 8) 

 0.13-0.22 m above the bottom of bed 501.1. Hesselbo etal. (2000) 

 did not find ammonites in the 1.8 m of strata below the base of the 

 Pliensbachian (ie. in the nodules of bed 500 and the shales of bed 

 499). Bairstow did not find ammonites in bed 500, but he collected 

 six specimens of Eoderoceras armatum from bed 499 in the middle 

 of the bay near Robin Hood's Bay town. These are well-preserved, 

 readily identifiable examples of the species (one is figured in PI. 8, 

 fig. 2), and Bairstow's records show that they were collected 0.15- 

 0.37 m above the base of that bed. A single E. armatum, less 

 well-preserved than those lower down, but still readily identifiable 

 with that species, was collected from Wine Haven high in bed 499, 

 only 0.15 m from the top. The thickness of strata across the 



Sinemurian/Pliensbachian boundary from which no ammonites have 

 been collected is thus reduced to only 0.36 m. 



JAMESONI ZONE, Taylori Subzone, beds 501.1-537. The base 

 of the subzone (and the Jamesoni Zone, and the Pliensbachian Stage) 

 is placed at the bottom of bed 501.1, which contains the lowest 

 occurrence of the characteristic genus Apoderoceras, and this is the 

 only horizon at which Bifericeras donovani Dommergues & Meister 

 occurs. Phricodoceras taylori and other species of Phrkodoceras 

 are present through much of the subzone and do not range higher. 

 Many examples of Gemmellaroceras tubellum are found near the 

 base of the subzone, and the larger species G. rutilans occurs in the 

 top part. A single specimen of Radstockiceras buvignieri was also 



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