162 Mr. S. P. Pratt on some neio specien of Ammonites. 



a nearly perfect condition, but from their flattened state it 

 is often difficult to determine their distinctive characters ; this 

 has however been attempted in the following descriptions, 

 which have been drawn up after an inspection of several 

 hundred specimens ; and of a few individuals, which, having 

 fortunately been found in indurated nodules in the clay, and 

 thus preserved fi*om compression, exhibit characters which 

 the usual state of the fossils do not afford. The specimens 

 described are partly from the authoi^'s collection, and partly 

 from that of the Bristol Institution, which possesses an ex- 

 tensive series of fossils found in the same locality, collected 

 by the zeal of Mr. S. Stutchbury. Some apology may seem 

 necessary for having employed proper names so extensively 

 in the designation of the species ; but in a genus, the general 

 characters of which are so similar, and in which the species 

 are so numerous, it is difficult to find characteristic distinc- 

 tions : this genus has also, by almost general consent, been 

 adopted to commemorate the names of individuals, who have 

 distinguished themselves either by their discoveries in the 

 science, or by their love and patronage of it, 



1. Ammonites Elizabethce. PL III. fig. 1, 2, 3, 4. 



Shell angular, arising from a series of spines on each dorsal 

 edge, and two rows of tubercles on the sides of the vo- 

 lution, one near the middle, another smaller and com- 

 pressed near the inner margin ; radiated, the rays varying 

 very much in number and elevation, curved or undulated, 

 but becoming angular near the aperture of the adult shell, 

 which has on each side a long, narrow, spatulate projec- 

 tion, the prolonged rays forming waves or loops on its 

 surface ; volutions six or seven, about f rds exposed ; 

 back narrow, concave, the rays passing over it and form- 

 ing low obtuse ridges ; siphunculus not visible. 



The number and length of the spines and tubercles, and the 

 mode in which they are combined with the rays, appear to 

 indicate several distinct species, but on closer examination it 

 is seen that all the varieties pass into each other, the same 

 specimen sometimes containing more than one form. 



The spines and rays vary from sixteen to upwards of sixty 

 on the last volution, and they are large and elongated in pro- 

 portion to the smallness of their number ; in the simplest 

 form, a single irregular ray, terminated on the dorsal edge by 

 a long sharp spine, connects it with the tubercles, scarcely 

 reaching the inner one in others ; two, three, and sometimes 

 four rays arise from the spine and unite in the middle tu- 



