]48 



AMMONITES Smithi. 



TAB. CCCCVI. 



Spec. Char. Depressed, ribed, and keeled ; 

 inner whorls few, almost wholly exposed ; 

 ribs slightly curved ; keel obtuse ; sides 

 flattened ; aperture oblong. 



A. BEAUTii UL pearly species that seldom acquires a di- 

 ameter of two inches ; the flatness of its last whorls, 

 distinguish it, independently of size, from others simi- 

 larly figured ; in its infancy, (see fig. 1.) it is wholly 

 plain and almost globose, with an umbilicus ; as it 

 grows, its ribs appear gradually in short risings near the 

 umbilicus ; the keel is next formed, and at length the 

 whorls assume their flat shape, and the ribs their full ex- 

 tent ; figs, 2, 3 and 4. 



Occurs sparingly dispersed through the same stone 

 as A. planicostatus* (tab. 73,) and is mentioned at p. 

 168 of Vol. I. 



This is named in honor of Mr. W. Smith, the Author 

 of a Geological map of England, &c. whose discovery of 

 the regular succession of the strata, and the means of 

 distinguishing them by their organized contents, has 

 laid the foundation for all our Geological knowledge of 

 England. 



1 have taken this opportunity of adding a portion of 

 the outer whorl of an old shell of A. planicostatus, (see 

 fig. 6.) to shew that by age it acquires spines upon the 

 sides of the flattened portion of each rib, a circumstance 

 that ouglit to he noticed in the specific character. 



Figs. 5, 6, and 7, are several states of A. planicostiitua. 



* .So the name should have been spelt 



