ARIETITES BISULCATUS. 277 



lobe narrow, one third longer and a little wider than the principal lateral lobe, having 

 on each side five slightly unequal digitations. Siphonal saddle one fourth wider than the 

 principal lateral lobe, and divided into three unequal parts by two unequal accessory lobes. 

 Principal lateral lobe, a little longer than wide, has three foliated branches on each side. 

 Lateral saddle nearly double the width of the principal lateral lobe, and divided into many 

 unequal lobules. Inferior lateral lobe nearly as wide as the principal lateral, and divided 

 into numerous unequal digitations. Auxiliary saddle half the size of the principal lateral 

 lobe, divided into several unequal foJioles. Auxiliary lobe narrow, descending much 

 lower than the others, and formed of two branches, the one external and the other inferior. 

 Affinities and Differences. — This Ammonite strongly resembles A. Bucklandi, Sow. ; 

 it is distinguished, however, by haying the whorls more quadrate, and the general form 

 more angular ; the forty to fifty ribs have each a tubercle near the outer border, from 

 whence they curve sharply forwards towards the sulcus. In A. Bucklandi there are about 

 twenty-four ribs, which gradually disappear on the siphonal area, and there are no tuber- 

 cles near the angle of the sulcus. It is distinguished from A. obtusus, to which it has a 

 general resemblance, by having narrower whorls, tuberculated ribs, and a much flatter 

 siphonal area. 



Locality and StratigrapUcal Position. — This species has been found in the Zone of 

 Arietites Bucklandi (Lower Lias) near Lyme Regis and Charmouth, on the coast of Dorset ; 

 at Weston near Bath ; in the deep cuttings of the Bristol and Birmingham Railway, near 

 DefFord, Bredon, Cheltenham, and Gloucester, Coombe Hill, Highnam, and Berkeley, 

 and in other localities in the Vale of Gloucester, The Warwick Museum contains 

 some fine specimens from the Lima-beds of the Lower Lias in Warwickshire; and 

 my late friend, Mr. John Leckenby, F.G.S., had several fine shells of this species 

 collected from the Lower Lias at Robin Hood's Bay, on the coast of Yorkshire, which 

 are now in the Woodwardian Museum, Cambridge. 



Foreign Localities. — Germany — in Swabia and Wiirttemberg (according to Professors 

 Quenstedt and Oppel), it is abundant in the Bucklandi-beds of Bodelshausen, Vaihingen, 

 Mohringen, and Gmiind. The Museums of Stuttgart and Tiibingen contain many fine 

 examples. In France from the same zone in the vicinity of Metz, (Moselle) ; and Avallon, 

 (Yonne). The Museum of Semur, Cote-d'Or; contains many fine shells from the Lower 

 Lias near that town. 



History. — The history of this species is curious and instructive ; towards the end of 

 the seventeenth century it was figured by Plot and Lister in this country, and by Lang 

 and Bourguet on the Continent. In 1787, it was first correctly described in the 'Ency- 

 clopedie Methodique ' by M. Bruguiere as A. hisulcata ; he recognised two distinct forms, 

 one with few ribs without tubercles, the other with numerous ribs having a 

 tubercle on each. Sowerby, in his ' Mineral Conchology,' in 1818, figured the former 

 as A. Bucklandi, the latter, in 1824, as Ammonites multicostata. Unfortunately this 

 author entirely overlooked the excellent work previously published on Ammonites by 



