236 Mr. H. Seeley on Ammonites 



side, which bifurcates. The dorsal saddle is unequally divided. 

 The superior lateral lobe has a few digits on each side, and two 

 terminal trilobed branches. 



Height If inch; width of umbiHcus \ inch. Height of 

 mouth I inch; width nearly f inch. 



This is one of those remarkable Ammonites which undergo a 

 transformation of ornamentation. The chai*acters described are 

 only those of the adult state. In a younger condition, the ribs 

 appear to have been alternately long and short, and to have 

 each passed over the back without a forward curve. 



The example figured is the only one I have seen. There is 

 no cretaceous shell that can be compared with it ; and one of 

 the few Ammonites having two ribs united to pass over the back 

 is a species from the Lias of Amberg, described by Miinster as 

 A. Fischeri. That, however, has no umbilical tubercles; the 

 ribs are wide and obtuse, and fewer, and the aspect more 

 compressed. 



Loc. Ashwell. Coll. University Museum. 



Ammonites Woodwardi. PI. XI. fig. 3. 



Few-whorled, inflated, with convex sides bearing spines, and 

 a round back. Umbilicus mostly higher than the whorl oppo- 

 site to the mouth, and appearing relatively high from the half- 

 embracing whorls enlarging but slowly : it is quite smooth and 

 rather deep ; but the sides are inflated, and round imperceptibly 

 into the sides of the whorl. 



Around the side of the whorl, midway between the back and 

 the umbilicus, is a row of some ten or eleven rather elevated 

 spines, from which slight inflations descend to the umbilicus, 

 and strong round elevated ribs arise to pass over the back. In 

 each tubercle are collected three ribs, but only two of them pass 

 over to the corresponding tubercle ; for the spines of one side 

 are placed a little between those of the opposite side, rather 

 than facing them, so making a zigzag, which does not, however, 

 strike the eye. The ribs, separated by spaces fully as wide, in 

 the more compressed forms, where the tubercles are a little be- 

 low the middle of the whorl, pass straight over the back ; but 

 in inflated forms the costse are noticeably arched forward; 

 and in this variety the tubercles are above the middle of the 

 side ; and consequently the back, which is very much broader, 

 is much less convex than in the less inflated form. There is no 

 area that can be named a side, the lateral spines dividing the 

 umbilicus from the back; thus defined, the back will be nearly 

 as wide as three-fourths the height of the umbilicus. 



The mouth is wider than high, shaped like a moon entered 

 on her fourth quarter. 



