from the Cambridge Greensand. 241 



very narrow; umbilicus rather more than half the height of the 

 last whorl. 



The umbilicus, which is angular, is bordered on the side 

 by about fifteen (somewhat elevated, but not very large) tubercles, 

 separated from each other by fully the width of their bases. 

 To each of these tubercles converge three or four ribs, two or 

 three of which generally die away on reaching the eminence. 

 The ribs are round, very gradually widen, and are separated by 

 sulcations about equally wide ; for the lower two-thirds of their 

 length they are straight, and then gracefully curve forward, 

 dying away either separately or uniting in twos in large expanded 

 dorsal tubercles, which occupy the whole of the back, bend a 

 little outwards, and (probably) somewhat resembled those of A. 

 auritus; they numbered about thirty on each side, and were 

 neither opposite nor regularly alternate. 



The mouth is high and narrow, with the sides converging not 

 unlike an Egyptian doorway ; it is more than twice as high as 

 wide. 



Height 2-f inches ; width of umbilicus -^ inch ; height of last 

 whorl ^ inch ; width of base of mouth -^ inch. 



The specimen described is the only one I have seen. Though 

 the shell is otherwise well preserved, the dorsal tubercles are all 

 broken off quite at their bases. A line of the last whorl, broken 

 away, extends two-thirds round the shell ; so that perfect speci- 

 mens were probably not less than 4 inches in diameter. 



The affinities of this form are very near to A. splendens, Sow., 

 very evident with A. serratus, Park, and not too distant to 

 recall the idea of ^. auritus, Sow. The close ribbing, large dorsal 

 tubercles, and compressed aspect sufficiently and severally dis- 

 tinguish it from all of them. 



Loc. Ashwell. University Museum. 



Ammonites auritus, Sow. 



«. A. auritus, Sow. M. C. vol. ii. pi. 134 ; D'Orb. T. C. vol. i. pi. 65. 



A. Guersanti, Pictet (not D'Orb.), Ores Vert, pi. 5. f. 7- 

 ^. A. Raulinianus, Pictet & Campiche, T. C; Ste. Croix, pi. 29; D'Orb. 

 pl.^68. T. C; Pictet, Gres Vert, pi. 7. fig. 2. 



As has already been seen, A. Fittoni passes into A. auritus; 

 and similarly A. auritus passes into the fossil figured by Pictet 

 and Campiche as A. Raulinianus, which is only a variety of the 

 A. Raulinianus of D'Orbigny. The A. auritus figured by 

 Sowerby is a more robust form than that of D'Orbigny, more 

 intermediate in the series, and consequently a convenient type 

 for our forms. 



The first form is a compressed shell, with the umbilicus half 

 as high as the mouth, which is nearly two-thirds as wide as 



Ann. ^f Mag. N, Hist, Ser. 3. Vol. xvi. 1 7 



