24b YORKSHIRE TYPE AMMONITES Mar. 



24. AMMONITES BIRDI, Simpson 

 (Plate XXIV) 



Original Description 

 " 94. A[mmonites] Birdi. [M. Simpson, 1843, pp. 49, 50.] 



[" III. Keel between two furrows. 

 " a. Furrows slight." p. 48.] 



" Depressed ; volutions 5, exposed ; radii very prominent, sharp, 

 separated by large concave spaces, nearly straight, then make a slight 

 turn from the aperture, and form a tubercle, make another turn towards 

 the aperture on the back, where they become obsolete ; keel very small ; 

 grooves on either side nearly obsolete ; aperture quadrate ; diameter 

 2 inches. 



" The radii on the rounded inner edge of the whorls are nearly 

 obsolete, then become gradually more and more prominent, until they 

 reach the outer edge, where the groove which separates them is very 

 deep. From the very ferruginous appearance of this specimen I judge 

 it to be from the iron stone bands ; another smaller specimen I possess, 

 is from a lower-bed in the series, and has merely an elevated Hne for a 

 keel, and the furrows obsolete. 



" [P. 50] — In naming this Ammonite, it gives me much pleasure to 

 call to remembrance an individual who, I believe, was the first in this 

 town [Whitby], that undertook geological investigations, and who, 

 together with the Rev. G. Young, contributed much to the advancement 

 of geological science in their Survey of the Yorkshire Coast." 



Additional Details 



Simpson, 1855, p. 92, omits " depressed " at beginning ; omits all 

 after " ironstone bands." 



Simpson, 1884, pp. 131, 132, the same as 1855 ' enters the species 

 in Middle Lias a, p. xv. 



Remarks 



Stages, conch, serpenticone ; periphery, 4, ornament, 5*. 



The carina is not crenulated ; the ribs are strong, distant and 

 slightly 8 shaped on the, side, indistinct with long forward sweep on 

 the periphery, shewing indistinct signs of being bifurcate at and beyond 

 the tubercle. There is only one tubercle, which is almost a spine. 



The specimen has been ground away obliquely on one side. The 

 ferruginous appearance which Simpson mentions is very conspicuous. 



Genus Paltopleuroceras, S. Bnckman, 1898, 453 ; family Amaltheidae. 



Result 



Paltopleuroceras birdi, Simpson sp. 1843, Domerian, spinatum- 

 zone, near Whitby. 



