AMMONITES. 27 



9. Ammonites Woollgari, Mantell. Plate XI, fig. 1 and 2. 



Ammonites Woollgari, Mantell. Fossils of the South Downs, t. xxi, fig. 16 ; t. xxii, 



fig- 7. 



— — Sowerby. Min. Con., t. 587, fig. 1. 



— — IfOrbigny. Prodrome de Paleontologie, p. 189. 



— — (not), VOrbigny. Pal. Franc., t. 108, fig. 1-3. 



— Cakolinus ? D'Orbigny. Loc. cit., t. xci, fig. 5, 6. 



A. testa subcompressd, costatd, tuberculatd, interrupts carinatd : junior e, costis 16-18 

 elevatis, tri-tuberculatis, dorso interruptis, carina dorsali profunde serratd ; adolescenti, 

 costis rarioribus ad dorsum uni-tuberculatis, carina dorsali obsoletd ; adultd, costis bi- 

 tuberculatis, tuberculis maximis, dorso concavo : umbilico lato .• aperturd oblongd. 



Shell compressed, ribbed, tuberculated, and keeled ; changing its form and ornaments 

 as it enlarges ; when two to three inches in diameter it has sixteen to eighteen sharp, 

 elevated ribs on the side of each whorl, each rib bearing three tubercles, one near the 

 umbilicus and two near the back; the back has a sharp and deeply serrated keel, the 

 serrations corresponding in number to the ribs : when about four inches in diameter, the 

 keel is less prominent, the ribs are fewer and nearly obsolete, and bear one enormous 

 tubercle at their dorsal end : as the shell continues to enlarge, the whorl grows broader, 

 and has two rows of ten very large tubercles on each side, one close to the umbilicus, the 

 other at the dorsal edge, the back has entirely lost its keel, and is smooth and hollow 

 between the dorsal tubercles : umbilicus large and shallow, with two thirds of the whorls 

 exposed : aperture at first oblong and narrow, ultimately nearly of equal height and 

 breadth. The septa have not been clearly seen, they appear to have four or five trifid 

 lateral lobes. 



Diameter of old shell, 1 foot ; width, 3 inches. 



A rare shell in the Middle and Lower Chalk of Sussex. 



There is hardly any species of Ammonite which undergoes so great a metamorphosis as 

 A. Woollgari ; the young and middle stages of growth were well figured by Dr. Mantell ; 

 the older stage is not often met with, the only specimen which I have seen is in Mr. 

 Baber's collection, but is too imperfect to figure. The shell described as A. Woollgari 

 in the ' Paleontologie Francaise,' has no resemblance whatever to Dr. Mantell's species ; 

 this error is pointed out by M. d'Archiac, in the ' Histoire des Progres de la Geologie,' 

 vol. iv, p. 347, note, and has been corrected by M. d'Orbigny in the ' Prodrome de 

 Paleontologie,' vol. ii, p. 188. In the latter work M. d'Orbigny quotes his A. Carolinus, 

 Pal. Fran?., t. 91, fig. 5 and 6, as the young of A. Woollgari ; which identification is very 

 doubtful, as the French shell has twice as many ribs, is less compressed, and has the keel 

 more completely separated from the ribs by two regular channels, than our species. 



