from the Cambridge Greensand. 235 



the young state, sometimes three); and there is a free rib not 

 descending quite so far as these, intermediate between each two 

 tubercles. The ribs, parted by spaces of about twice their width, 

 are rather small and obtuse, becoming relatively less elevated 

 and narrower with age. At a third of the width of the side from 

 the back all the ribs are parted by regular distances, but from 

 about that point two of them converge towards a tubercle on 

 the back. The intermediate ribs, which do not pass over the 

 back, terminate where the back and side pass into each other. 



The back is about half as wide as the umbilicus is high, and 

 supports on the last whorl a row of spines one-fourth more nu- 

 merous than the lateral tubercles. They are short and large, 

 having for the base the whole width of the back, are directed 

 forward, and get steadily higher. They are an adult character, 

 the ribs passing over the back till the specimen gets of more 

 than nine lines diameter. 



The mouth, less than half the shell's diameter, is about a 

 fourth higher than wide. 



The septa are obliterated ; they were simple, with a small 

 inferior lateral lobe, and below it three small accessory lobes. 



A slight inflation extends all round one side of the whorl ; 

 but, from the near resemblance the shell has to Ammonites 

 glossonotus, I am not inclined to give that weight to the distor- 

 tion it otherwise would have. 



The late Dr. S. P. Woodward, in 1862, regarded this shell as 

 a monstrosity of Ammonites lautus, Sow., — a view with which I 

 cannot agree. 



Ammonites glossonotus. PI. X. fig. 4. 



Few-whorled,discoidal, moderately compressed ; back rounded; 

 umbilicus moderately large. 



Around the umbilicus are (about ten) prominent tubercular 

 spines, from each of which commonly arise two ribs, and an- 

 other is generally placed in each of the hollow spaces inter- 

 mediate between the tubercles. These ribs are elevated, narrow, 

 and not nearly so wide as the spaces between them, which are 

 of about equal width. Two of the ribs ascend the side of the 

 shell, nearly parallel to each other,* for two- thirds of its height, 

 when the hinder one bends rather suddenly forward so as to 

 unite, on the side of the back of the shell, with the front one, 

 which curves forward slightly ; united, they pass over the back 

 as a thick, elevated, tongue-like fold extending forward. Rarely 

 a rib passes over the back singly. 



The mouth, about three-fourths as wide as high, is shaped 

 like an ass-shoe. 



The septa are obscure, but appear to be unsymmetrical. The 

 dorsal lobe is short, nearly square, and has a branch on each 



