STEPHANOCERAS COMMUNE. 



473 



the equivalent horizon in Germany. Species of Stephanoceras are found also in the 

 Kelloways rock and in the clay bed interposed between it and the dark clays at the base 

 of the Oxfordian. 



Stephanoceras commune, Sowerby. PI. LXXXIII, figs. 3 — 4 ; PI. LXXXIV, figs. 



1—3; PI. LXXXVII, figs. 9, 10. 



Cornu-Ammonis, 

 Ammonites communis, 



angulatus, 



Nautilus annularis, 

 Ammonites communis, 



— annulatus, 



— annularis, 



communis, 



Planites BIFIDUS, 

 Ammonites communis, 



— annularis, 



— communis, 



Stephanoceras commune, Neumayr 



Lister. Hist, animal, PI. vi, fig. 5, 1678. 



Sowerby. Min. Conch., vol. ii, p. 10, pi. 107, fig. 3, 1815. 



— Ibid., vol. ii, p. 9, pi. 107, fig. 1, 1815. 



ReinecTce. Nautil. et Argon., pi. vi, figs. 56, 57, 1818. 

 Keferstein. Catal., 1819. 

 Schlotheim. Petref., p. 61, No. 2, 1820. 

 — Ibid., p. 78, No. 32, 1820. 



Young and Bird. Yorksh. Coast, p. 246, pi. xii, fig. 3, 



1822. 

 Haan. Amra. etGoniat., p. 86, No. 13, 1825. 

 Phillips. Yorksh., p. 163, 1829. 



Zieten. Versteiner. Wiirtemberg., p. 9, pi. vii, fig. 2, 

 1830. 

 — Ibid., p. 14, pi. x, fig. 10, 1830. 

 Si?npson. Monogr. on Ammon., p. 18, 1843. 

 d'Orbigny. Pal. Fr., Terr. Jurass., p. 336, pi. 108, 



1842. 

 Quenstedt. Die Cephalopod., p. 172, pi. xiii, fig. 8, 1846. 

 Der Jura, p. 251, 1858. 

 Zeitsch. Deutgeol. Gesell., p. 916, 1875. 



Tate and Blake. Yorksh. Lias, p. 299, 18; 



Diagnosis. — Shell discoidal, slightly compressed; whorls round and well costated 

 on the area and sides ; lateral costse 50, straight and directed obliquely forward, 

 at the side of the area they divide into two branches which arch forward over the area 

 and unite with those from the opposite side. Aperture orbicular and slightly grooved, 

 embracing the whorl. 



Dimensions. — Transverse diameter 83 millimetres ; height of last whorl 20 milli- 

 metres ; width of last whorl 20 millimetres ; width of umbilicus 48 millimetres. 



Description. — Shell discoidal and slightly compressed ; whorls feebly involute, round, 

 and gently flattened on the sides ; the latter covered with from forty-five to fifty sharp, 

 narrow costae, commencing at the spiral suture and ascending obliquely forward two thirds 

 of their length, when they regularly bifurcate without a trace of tubercle, and pass over the 

 siphonal area ; one of the two loops passes entire, whilst the second is often not com- 

 plete at the point of bifurcation. The whole of the costse of the area describe arches, 



61 



