75b YORKSHIRE TYPE AMMONITES— II August 



75. AMMONITES TRANSFORMATUS, Simpson 

 (Plate LXXV) 



Original Description 

 " 164. A[mmonites] transformatus. [M. Simpson, 1855, P- 91.] 



[" III. Keel between two furrows. 

 '* a. Furrows slight." p. 90.] 



" Volutions 5, exposed, outer whorl J the diameter ; radii strong, 

 prominent, sharp, separated by rather wide concave spaces, nearly obsolete 

 on the back, straight until they reach the outer margin of the whorls, 

 where, on the last whorl, they form a slight knob, and suddenly bend 

 towards the aperture ; keel much depressed, furrows on either side slight ; 

 aperture quadrate ; diameter ~l\ inch. 



"The inner whorls of this species are destitute of any dorsal keel 

 or furrow, and have a good deal the characters of A. arcigerens, though 

 by no means so numerous and slender ; but as they increase in size they 

 have gradually formed upon the back a distinct elevated line, which 

 ultimately becomes a depressed but distinct keel between two slight 

 furrows ; the radii towards the aperture beccme stronger, and form 

 distinct knobs on the outer margin of the whorl, when they greatly 

 resemble those of A. Hawskerensis. I have now seen a good number of 

 specimens, which have been obtained from lias boulders in the alluvium 

 on the Holderness coast, and some also from the lower lias at R.H. Bay." 



Simpson, 1884, 130, 131, the same. 



Remarks 



Proportions : 40, 35, 36, 38 : platy-, pachygyral, latumbilicate. 



Stages, conch, serpenticone ; periphery, 4 ; ornament, 1, 3, 4, 5. 



About half a whorl of the type is body-chamber, without test. 



Genus, Agassiceras, Hyatt (I, it) ; family Arietidse. Geological 

 position, according to Blake, (1876, 288, under Ar. sauzeanus), zone of 

 A. Bucklandi. 



The differences between Am. transformatus and Am. halecis (see 

 p. 75c) are small. In the former the coiling is a little slower, the umbilicus 

 slightly larger, the periphery rather more definitely squared, and the keel 

 a little less prominent. 



(t The holotype (Whitby Museum, No. 279) bears a faded label: 

 A transformatus, Lias boulder, Holderness Coast, Simpson." 



Result 

 Agassiceras transformatum, Simpson sp. 1855, [Sinemurian, 

 gmuendense zone], Alluvium, Holderness Coast. 



