ARIETITES OBTUSUS. 293 



Affinities and Differences. — The affinities of A. Turneri to A. Brookii are so 

 numerous, and the differences between them so few and inconsiderable, that I consider 

 the question of their specific distinction one which requires further consideration ; the 

 affinities are more fully pointed out in the description of A. Brookii. 



Locality and Stratigrap Ideal Position. — The specimen figured was collected from a 

 light-coloured clay and limestone in the deep cutting of the Bristol and Birmingham 

 Railway, near Bredon, and was associated with A. Bonnardii, d'Orbigny, A. semicostatus, 

 Y. & B., and several other Molluscs, with many fragments of the stems and side arms of 

 Tentacrinus tuberculatus, Miller, and Cidaris Edwardsii, Wright. 



Arietites obtusus, Sowerby. PI. XXI, figs. 1 — 5. 



Ammonites obtusus, Sowerby. Mineral Conchol., vol. ii, p. 151, tab. 167, 1818. 



— Smithi, Sowerby. Ibid., vol. iv, p. 148, tab. 406, 1823. 



— obtusus, Phillips. Geology of Yorkshire, p. 136, 1835. 



— — Simpson. Monogr. of the Ammonites of the Yorksh. Lias, p. 50, 



1843. 



— — d'Orbigny. Paleontologie Francaise, Terr. Jurassique, pi. xliv, 



p. 191, 1842. 

 ■ — Turneri, Quenstedt. Flbzgebirge Wurtembergs, p. 156, 1843. 



— — Quenstedt. Cephalopoden, p. 77, tab. iii, fig. 19, 1846. 



— obtusus, Chapuis et Dewalque. Fossiles Terr. Second. Luxembourg, pi. 



iv, fig. 3 ; pi. v, fig. 1, p. 39, 1853. 



— — Simpson. Fossils of the Yorkshire Lias, p. 92, 1855. 



— — Oppel. Jura-Formation, p. 83, 1856. 



— Turneri (obtusus), Quenstedt. Der Jura, p. 95, 1858. 



— obtusus, Dumortier. Depots Jurass. du Bassin du Rhone, t. ii, p. 122, 



1867. 

 Arietites — Tate and Blake. Yorkshire Lias p. 287, 1876. 



Diagnosis. — Shell thick, compressed, and tricarinate ; carinas obtuse ; whorls sub- 

 rotund, with twenty-five to thirty lateral ribs, which curve toward the aperture, are thick 

 and obtuse, vanishing near the outer carina ; lateral septa three-lobed ; shell covered on 

 all sides with fine longitudinal lines, twenty-eight on each side of the whorl, producing 

 a series of punctations where they intersect similar transverse lines ; .aperture rotundo- 

 compressed. 



Dimensions. — The usual size is from 150 to 200 millimetres in diameter, but it attains 

 300 to 400 millimetres. Dimensions of the specimen figured in PI. XXI, figs. 1, 2, 

 transverse diameter 155 millimetres ; height of the last whorl at aperture 65 millimetres ; 

 width 58 millimetres; width of the umbilicus 55 millimetres. The relative dimensions 



