388 



THE LIAS AMMONITES. 



Ammonites oxynotus, von Rauer. Jahrbuch der k. k. geol. Reichsanstalt, iv, 



p. 754, 1853. 



— POLYOPHYLLUS, Simpson. Fossils of the Yorkshire Lias, p. 81, 1855. 



— RoBiNSONi, — Ibid., p. 83, 1855. 



— BucKii, — Ibid., p. 84, 1855. 



— DEJECTUS, — Ibid., p. 85, 1855. 



— oxYNOTtis, vonHauer. Cephalopod. derNord6st.Alpen,Deukschr.Akad. 



Wissensch., p. 48, Taf. xiii, figs. 4 — 10, 185C. 



— — Oppel. Die Juraformation, s. 85, 1856. 



— — Wright. Quart. Jour. Geol. See, vol. xvi, p. 407, figs. I, 



2, 1860. 



— — Bumortier. Depots Jurass. du Bassin du Eh6ne,ii, p. 143, 



tab. xxxiii, figs. 1 — 5, 1867. 

 Amaltheus — Tate and Blake. The Yorkshire Lias, p. 291, 1876. 



Diagnosis. — Shell discoidal, very much compressed; whorls five, extremely involute, 

 inner volutions scarcely exposed ; outer whorl very high, half the diameter of the shell ; 

 inner margin rounded, sides convex, outer margin thin, sharp, and catting ; sides shghtly 

 convex, with thirty to forty irregular folds limited to the middle, and which at two thirds 

 of the whorl bifurcate, the branches bending forward at an acute angle towards the 

 aperture ; umbilicus very narrow, aperture lanceolate. 



Dimensions. — This species varies much in size^ and in old age attained a consider- 

 able diameter. I have collected specimens from one inch and a half, or 40 millimetres, 

 up to one foot, equal 300 millimetres, in diameter, with the body-chamber, all of which are 

 in my collection. I consider the shell figured (PI. XLVI, figs. 4, 5, 6) as a good type 

 form of this species in middle age, and which gives the following measurements : — Trans- 

 verse diameter 90 millimetres; width of umbihcus 18 millimetres; height of aperture 

 51 millimetres ; greatest width 18 millimetres. 



The late Monsieur Dumortier collected a number of specimens of different sizes from 

 Lournand, Jambles, St. Helene, St. Fortunat, and in his excellent work has given the 

 measurements of six of these for comparison.^ 



Diameter. 



Height of last whorl. 



Thickness of last whorl. 



Size of umbilicus. 



20 mill. 



45/100 



2.'./100 



28/100 



71 „ 



45/100 



17/100 



18/100 



86 „ 



46/100 



17/100 



19/100 



185 „ 



47/100 



20/100 



23/100 



220 „ 



45/000 



12/100 



20/100 



330 „ 



44/000 



23/100 



21/100 



' Depots Jurassiques du Bassin du Rhone,' ii, p. 143. 



