48 FOSSIL MOLLUSCA OF THE CHALK. 



38. Ammonites leptophyllus, Sharpe. Plate XXI, fig. 2, and Plate XXH, fig. 1. 



Ammonites Lewesiensis, Sowerby. Mineral Conchology, t. 358. 



— — IfOrhigny. Prodrome de Paleontologie, vol. ii, p. 189. 



A. testa discoided, compresm, undidato-costatd : anfractibus lateraliter costatis^ dorso 

 IcBvibus : costis numerosis, pauliim elevatis : dorso rotundato Icevi, lined angusta impresso .- 

 vMbilico parvo : aperturd elevato-ellipticd : septorum lobis lateralibus ramosissimis, ramis 

 irregulariter alternantibus. 



Shell discoidal, flattened at the sides, rounded at the back : sides of the whorls crossed 

 by numerous radiating undulations, or low, broad ribs, which commence at the umbilicus, 

 and die out before they reach the back : umbilicus small, bounded by steep sides, allowing 

 more than half the inner whorls to be seen : back smooth and rounded, marked with a 

 narrow, impressed line : opening high and narrow : lobes of the septa much subdivided ; 

 the superior lateral lobe very large, w^ith numerous irregularly alternate branches, ending 

 in long, pointed digits. In very old specimens the undulations are very faint, and 

 gradually disappear. 



This species reaches a diameter of more than 2^ feet. The proportions of the specimen 

 figured are — diameter, 12 inches; height of the last whorl, 5 inches; width of the 

 aperture, 3 inches. 



Found in the Upper Chalk of Brighton, Ramsgate, Greenhithe, &c. ; but, from the 

 softness of the chalk in which it occurs, it is very seldom met with in good preservation. 



This is not the species originally named by Dr. Mantell A. Leicesiensis, nor is it the 

 species pubhshed under that name by M. D'Orbigny in the ' Paleontologie Francaise,' 

 which is now called A. Gollevilleiisis ; but in his ' Prodrome de Paleontologie,' that author 

 has so far corrected himself as to separate the last-named species from the one here 

 described. 



As there have thus been three species passing under the name of A. Leicesiensis, it is 

 impossible to know what is meant when this name is cited in geological works ; a com- 

 parison of the three species is given, after the description of A. Lewesie?ms. 



39. Ammonites Gollevillensis, D'Orb. Plate XVII, fig. 2. 



Ammonites Lewesiensis, D'Orbigny. Paleont, Fran9. Terr. Cret., t. 101. 



— — Id. Prodrome de Paleontologie, vol. ii, p. 212. 



A. testa discoided, compressd, costatd: anfractibus lateraliter Icevibus, dorso cosfatis: 

 costis brevibiis, numerosis, cequalibus, ad dorsum interruptis : dorso rotundato, costato, lined 



