52b YORKSHIRE TYPE AMMONITES May 



52. AMMONITES SOLITARIUS, Simpson 

 (Plate LII) 



Original Description 

 " 169. A[mmonites] solitarius. [M. Simpson, 1855, p. 93.] 



" [III. Keel between two furrows, p. 90. 

 " b. Furrows distinct." p. 93.] 



" Volutions 5, exposed, outer whorl \ the diameter of the shell, 

 sides flatted ; radii numerous, equal, prominent, nearly straight to the 

 outer margin of the whorl, then suddenly bend towards the aperture, 

 equal to the intervening concave spaces ; keel rounded, strongly crenated, 

 the furrows on either side nearly obsolete ; aperture oblong quadrate ; 

 diameter ij inch." 



" On the inner whorls of this ammonite may be seen a row of tubercles, 

 at a short distance from the outer margin. The shell, as far as can be 

 observed, appears very thin, and quite smooth and shining ; but very 

 little of it remains, and the cast is roughish, exhibiting the ramifications 

 of the septa rather rounded, and very numerous, covering nearly the 

 whole surface of the shell with their meanderings. — L.L. ; R.H.B ; 

 [Lower Lias, Robin Hood's Bay] ; Mr, Morley's Col." 



Additional Details 



Simpson, 1884, 133, places " L.L., R.H. Bay " at end of first par. 

 instead of 2nd ; omits the three words at end of description. 



Remarks 



Stages, conch, serpenticone ; periphery, 5, crenulate ; ornament, 4c, 

 (5* inner whorls). This form illustrates the passage from tuberculate 

 to costate species. 



Genus, Paltopleuroceras, S. Buckman, 1898, 453 ; family, Amaltheidre. 

 The geological position given by Simpson is certainly incorrect : the 

 species would be from the top of the Middle Lias. 



Result 



Paltopleuroceras solitarium, Simpson sp. 1855, Domerian, 

 [spinatmn zone], Robin Hood's Bay? near Whitby. 



