from the Cambridge Greensand. 237 



The septa are simple, the dorsal lobe being square, with two 

 small terminal branches. There are two lateral lobes, one above 

 and one below the spines. 



Diameter lg- inch, with septa to the end. 



It also occurs in the Gault of Folkestone; and is not easily 

 distinguished from one described by Von Hauer, from the Lias, 

 as A. spinescens. 



The name has for some years been associated with that of the 

 late Dr. S. P. Woodward, under whose friendly guidance it was 

 my privilege to gain a knowledge of shells. 



Ammonites coelonotus. PI. X. figs. 2 & 3. 



Few-whorled, much compressed, with nearly flat though 

 slightly inflated sides ; back rounding, with a deep mesial 

 groove ; umbilicus as high as the whorl at the opposite side to 

 the mouth. 



The umbilicus is shallow, but well defined, its narrow hori- 

 zontal spiral boundary forming right angles with the vertical 

 sides. Around this umbilical angle are about twenty-five little 

 eminences — the thickened origin of the ribs. From these points 

 the ribs ascend towards the back, being directed forward at a 

 considerable curve for about one-fourth- of their length. Each 

 rib then, on the side towards the mouth, gives off a branch, 

 and these bend back a little, so as to be for about half their 

 length perpendicular, and then again curve forward in a small 

 arc, passing on to the back, where they continue to be directed 

 towards the mouth till terminating on the margin of the dorsal 

 groove at the distance of the fifth rib in front of their own 

 straight part. The ribs are wide, rounded, and depressed, and 

 separated by sulcations of about half their width, w r hich taper 

 gradually both towards the back and umbilicus. 



The back is half the width of the umbilicus, with a deep 

 mesial groove, towards which the sides gently round ; the sides 

 of the sulcation make a sharp angle with the back. 



The mouth at its base is two-thirds as wide as high ; at its 

 upper part, where the sides begin to round into the back, it is 

 half as wide as high. 



The septa of this shell are remarkable for the small size of the 

 dorsal lobe, which is contained in the dorsal groove, and bifur- 

 cates. There are two lateral lobes : the superior lateral is twice 

 as wide and half as long as the dorsal lobe ; there are two 

 notches on each side of it, and at its termination three branches, 

 the central of which has three digits. The dorsal saddle, which 

 is more than twice as wide as the superior lateral lobe, is divided 

 into two subequal parts. 



This is one of the less common forms ; but the few specimens 



