74 b YORKSHIRE TYPE AMMONITES— II May 



74. AMMONITES NITESCENS, Young & Bird 

 (Plate LXXIV) 



Original Description 



[Young & Bird, 1828, p. 257] 



" Sowerby's A. striatulus, Tab. 421.1, is found in similar nodules 

 [to A. semicostatus] at Peak, and has been recently discovered in the 

 Glazedale dogger. We have known it for some years, and given it the 

 name A. nitescens, from its smooth, shining aspect. It has a blunt keel ; 

 aperture oval ; sides marked with faint sigmoidal ribs, and slight striae 

 of the same form. — There is a rare ammonite in the lias bands, nearly 

 corresponding with this in shape, but flatter on the back, having only 

 a faint appearance of a keel ; and smoother also on the side, the shell 

 being without striae. The name A. nitescens may now be appropriated 

 to this last species." 



Remarks 



Proportions, 93, 29, 21, 44 : Subplaty-, subleptogyral, perlatum- 

 bilicate. 



Stages, conch, serpenticone ; periphery, 4c, slight depression each 

 side of a small keel ; ornament, 5* ; coarse distant ribs, each with a blunt 

 nodus on edge of periphery ; peripheral projection fairly long. 



^ Genus, Seguenziceras, Levi, 1896 ; family, Hildoceratidae. Geological 

 position, " Zone of A. margaritatus " (Blake, 1876, 303) ; M.L., t, Hawsker 

 (Simpson, 1884, *25). 



Result 



Sequenziceras nitescens, Young & Bird sp. 1828, Domerian, 

 algovianum zone, [Hawsker], near Whitby. 



