AMMONITES. 29 



projecting ribs. I have named it after Robert A. C. Austen, Esq., F.R. and G.S., in whose 

 neighbourhood at Chilworth, this Ammonite is very abundant. 



12. Ammonitis planulatus, Sowerby. Plate XIT, fig. 3 and 4. 



Ammonites planulatus, Sowerby. Mineral Conchology, t. 570, fig. 5. 



A. testa discoided : anfractibus complanatis, externe costatis, interne Icevibus ; sulcis 5 

 transversis subflexuosis, impressis ; costis numerosis, hrevibus : dorso rotundato transversim 

 costato : umbilico magno ■■ aperturd semi-ovatd : lobis septorum lateralibus incequaliter 

 bifidis. 



Shell discoidal, with four or five whorls flattened on the sides, and rounded on the 

 back, crossed by five deep, slightly flexuous furrows, between which are many short slight 

 ribs, which cross over the back and only reach the middle of the side of the whorl : 

 umbilicus large and well-defined, leaving three fifths of the inner whorls visible : aperture 

 semi-oval : lateral lobes of the septa unequally bifid. 



Diameter, 2^ inches. 



Rare in the Grey Chalk near Lewes and Bonchurch ; common in the Upper Green 

 Sand near Cambridge. 



I have seen but few specimens of this species from the Chalk, and as that originally 

 figured by Sowerby is , badly preserved and somewhat crushed, and does not show the 

 margins of the septa, a figure is added of a well preserved internal cast from the Upper 

 Green Sand. M. d'Orbigny unites to Sowerby's species, under the name of A. Mayorianus, 

 an Ammonite found in the Lower Green Sand and Gault of France, which differs from 

 our species in having only four transverse furrows instead of five, the furrows more 

 flexuous, and bounded by stronger swellings, and the cast entirely smooth; it has, 

 moreover, the lateral lobes of the septa trifid, which distinguishes it from Sowerby's 

 species. I cannot, therefore, regard his species as identical with ours. M. d'Orbigny's 

 reason for dropping Sowerby's specific name, that it had been previously used by 

 Schlotheim for another species, is also insufficient : since Schlotheim's species being 

 abandoned by every one, including M. d'Orbigny himself, ' Terr. Jurass.,' vol. i, p. 509, 

 the name remains open for the next species to which it has been applied, which is the one 

 here described. 



13. Ammonites catinus, Mantell. Plate XIII, fig. 1. 



Ammonites catinus, Mantell. Fossils of the South Downs, t. xxii, fig. 10. (Not t.xxii, 

 %. 5.) 



A. testa inflatd : anfractibus panels, latis, rotundatis, lateribus 10-12 tuberculatis, dorso 

 lavibus : umbilico lato, pro/undo : aperturd transversa, semi-circidari. 



Shell gibbous, with three or four broad whorls, depressed and smooth on the back, 



