97b YORKSHIRE TYPE AMMONITES— II Jan. 



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V "L 



97. TILTONICERAS COSTATUM, S. Buckman 

 (Plate XCVII) 



Original Description 

 [1913, Y. T. A., II, viii] 



" T. costatum differs from T. acutum in being more distinctly and 

 strongly costate." 



Additional Details 



Proportions, 29, 46, 29, 29 ; perplaty-, subpachy-gyral, sub- 

 latumbilicate. 



Stages, conch, platycone ; periphery, 3 ; ornament, 4. 



The whorls are broad, the ribs are distinct, slightly flexed on the 

 side, continued as fine lines with a very long forward sweep on to the 

 periphery, which carries a rather massive, fairly prominent carina. 



The inner margin falls steeply, with only the least sign of concavity. 



Remarks 



The costae are stronger and more persistent than in H. acutum, 

 Tate, and the umbilicus is slightly larger, especially in the inner whorls. 

 This species is in the costate stage ; T. acutum is in the striate stage, 

 with the costate stage in the inner whorls. 



In the example of T. costatum depicted in PI. XCV, fig. 1, the portions 

 marked white to show the radial curves cover two costae, so do the inter- 

 mediate dark parts. 



Genus, Tiltoniceras, nov., of which T. costatum, type, is the genotype ; 

 family Hildoceratidae . 



Geological position, in the Transition Bed, which is just above the 

 zone of Paltopleuroceras spinatum. 



Result 



Tiltoniceras costatum, S. Buckman, 1913, Domerian, acutum 

 zone, Tilton, Leicestershire. 



Note 



Figs. 3, 4, Plate XC, depict a paratype from the same place in the 

 Collection of Mr. J. W. Tutcher, who has photographed it, and marked in 

 the radial line. It is a larger specimen, showing the ribs becoming stronger 

 and broader. Its proportions are 37, 44, 28, 26. Both types were 

 originally collected by the late E. Wilson, F.G.S. 





