164 Mr. S. P. Pratt on some new species of Ammonites. 



5. Ammonites Lonsdalii. PI. V. fig. 2. 

 Shell discoidal, radiated (when young) with numerous waved, 

 well-defined, raised lines, which become more obtuse and 

 fewer as the shell increases in size ; near the aperture 

 they pass into fine strise ; the rays rise from the dorsal 

 edges, and scarcely reach the middle of the side ; the 

 aperture forms a regular concave termination, except on 

 the inner edge, where it bends back like the handle of a 

 sickle ; volutions |^rd exposed, the last more than half the 

 diameter of the shell. 



6. Ammonites fluctuosus. PI. VI. fig. 1 and 2. 



Shell discoidal or lenticular, radiated (when young) with nu- 

 merous sharp raised lines, which are alternately long and 

 short ; the short combining in twos or threes with the 

 longer ones about the middle of the side_, some remain- 

 ing distinct : as the shell advances in age the inner half 

 of the long rays becomes much thickened, until they 

 form obtuse elevated ridges, with broad, concave, smooth 

 spaces between, the short rays gradually disappearing ; 

 volutions numerous, f rds exposed ; shell reaching 6 

 inches in diameter, without any appearance of projecting 

 aperture. 



7. Ammonites Brightii, PI. VI. fig. 3, 4. 



Shell discoidal, nearly smooth, but having several flat, obtuse 

 ridges arising from the dorsal edge, which combine a 

 little beyond the middle of the volution into a com- 

 pressed elongated tubercle which reaches the inner mar- 

 gin ; the tubercles are about one-third as numerous as 

 the ridges, and meet them in a rounded right angle : in 

 the young shell they are hardly visible, and also become 

 obsolete near the aperture, the sides of which suddenly 

 contracting to about one-third, again expand into a trans- 

 verse oval projection, finely waved or striated ; the back 

 of the shell also projects in a point, and forms with the 

 sides a concave arch ; a sharp ridge on the back marks 

 the siphunculus ; volutions about 7? f rds exposed. 



8. Ammonites Gulielmi, Sowerby, Min. Con., pi. 311. 

 This species differs considerably from the description given 

 by Sowerby, although there can be no doubt of its being the 

 same shell ; when fully grown to about 5 inches in diameter, 

 the inner thickened rays form strong, elevated, compressed 

 spines or tubercles. 



