lob YORKSHIRE TYPE AMMONITES Mar. 



1910 



10. AMMONITES SUBCONCAVUS, Young & Bird 

 (Plate X) 



Original Description 

 [Young & Bird, 1828, p. 266.] 

 " No. 5, PI. XIII, also from the lias bands, very nearly coincides 

 with A. concavus, Tab. 94.2, [Sowerby] having a round cavity in the 

 centre, and ribs nearly in the shape of reaping hooks. It is, however, 

 thicker at the back, and has the keel less prominent ; and the aperture 

 is not triangular or sagittate, but oblong quadrate. As it differs in these 

 respects from Sowerby's shell, we may name it A. subconcavus." 



Additional Details 



Young & Bird, 1822, p. 251, had described this species as A. con- 

 cavus, Sowerby (see No. 11), and figured it PI. xiii, fig. 5, of that 

 edition. 



Remarks 



Stages, conch becoming oxycone ; periphery, 4c ; ornament, 4c. 



The sides of whorls are convergent from about the umbilical border ; 

 thus the aperture is really somewhat sagittate : some dislocations are 

 answerable for Young & Bird's description, and for the appearance 

 of the aperture now. 



The septate keel is lost ; there are small furrows beside it. 



The genus is Pseudolioceras, S. Buckman, 1888, p. 81, family Hildo- 

 ceratidae. 



The geological position, Simpson says, is " U.L. 6," (1884, 111). 



Result 



Pseudolioceras subconcavum. Young & Bird sp., 1828, 

 Whitbian, falciferum-zone, near Whitby. 



