AEGOCERAS VALDANI. 357 



whorls are not so high, the ribs are narrower, sharper, and more bent, and the intercostal 

 valleys are much wider and more concave, the siphonal area is likewise much changed 

 by the presence of a central carina which passes longitudinally between the ribs and con- 

 nects them with each other. The inner whorls are absent ; this body-chamber forms a 

 striking contrast to the figure given in PI. LII, figs. 1 and 2 ; the small specimens figured 

 in both plates very much resemble each other in the thickness and roundness of the 

 whorls and the sharpness of the ribs as shown in the mould. 



Locality and Strati (jrapldcal Position. — Professor Blake says that this Ammonite 

 comes from a different horizon to that in which Aeg. Jamesoni lies, and assigns the base 

 of the zone of AmaltJieus oxynotus in Robin Hood's Bay as its true geological position. It 

 was likewise from the same locality and horizon that the Rev. J. E. Cross obtained the 

 large specimens he has so kindly communicated for this work. 



Aegoceras Valdani, d'Orbiyny. PI. XXXVIII, figs. 1, 2, 3, 4 ; PI. LXIX, figs. 2, 



3 and 4. 



AMMomTES BiPUNCTATUS, Romcr. Versteiiier. des Nord-Deutsch. Oolitheu-Gebirges, 



p. 193, 1836. 



— BiHCHi, Quenstedf. Fltizgebirge Wiirtembergs, p. 173, 1843. 



— Valdani, d'OrLigny. Paleontol. Francaise ; Terr. Jurassique, tome i, 



p. 255, pi. 71, 1844. 



— — Quenstedt. Cephalopoden, p. 90, tab. v, fig. 3, 1849. 



— — Ciebel. Fauna der Vorwelt, vol. iii, p. 683, 1852. 



— — Chnpuis et Bewahpip. Terr. Second. Luxembourg, Mem. 



Cour. Acad. Belgique, t. xxv, p. 47, 

 pi. vi, fig. 3, 1853. 



— — Oppel. Mittlere Lias Scbwabens, Jahreshefte Wurttemoerg, 



p. 78, tab. 2, fig. 2, 1853. 



— — Studer. Geologie der Schweiz, ii, pp. 26, 32, 1853. 



— — Meneghini. Nuovi Fossili Toscani, pp. 10, 32, 1853. 



— — Merian. Verband. Naturforscb. Gesellsch. Basel, vol. i, p. 



79, 1854. 



— — Fori Hauer. Cephal. Lias N.-O. Alpen, Dcnk. Akad. Wis- 



seu., t. xvii, figs. 13, 15, p. 53, 1856. 



— BIPUNCTATUS, 0/j^e/. Die Juraformation, p. 160, 1856. 



— Valdani, Quenstedt. Der Jura, pi. xvi, figs. 2, 3, p. 131, 1858. 



— BIPUNCTATUS, Dumortier. Dt^pots Jurass. Bassin du Rhone, torn, iii, 



p. 70, 1869. 



Diagnosis. — Shell discoidal, compressed, carinated ; whorls flattened on the sides, with 

 simple, straight ribs, which terminate in two rows of tubercles, one row situated at the 



