ARIETITES SAUZEANUS. 281 



for Sowerby says in his description of A. Turneri, — " The more exposed whorls, squarish 

 aperture, and differently curved radii, distinguish this from A. Brooki, to which it bears 

 a strong resemblance." If a larger series of both forms could be obtained, it is probable 

 it would be found that they merged by a gradual series of gradations into one species ; 

 but, for the sake of convenience and easy reference, until more facts are brought to light, 

 I have thought it best to figure good type forms of each, from which it will be seen that 

 the affinities are many and the differences few and immaterial. 



Locality and Stratigraphical Position. — Arieiites Brooki is found in fine preserva- 

 tion, with the shell complete, at Lyme Regis, in beds of shale and Lower Lias Limestone ; 

 sometimes it is enclosed in crystalline masses of sulphuret of iron. It is on the whole 

 a rare Ammonite. 



Arietites Sauzeanus, oV Orbigny. PI. VIII, figs. 1 to 6. 



Ammonites Sauzeanus, d'Orbigny. Paleontologie Francaise, Ter. Jur., p. 304, 



pi. xcv, figs. 4 — 5, 1842. 



— eesupinatus, Simpson. Monogr. of the Ammonites, p. 15, 1843. 



— spinakies, Quenstedt. Der Jura, p. 69, pi. vii, fig. 4, 1S58. 



— tbansformatus, Simpson. Foss. of the Yorkshire Lias, p. 91, 1855. 



— Sauzeanus, Wright. Monograph on the Asteroidea, Pal. Soc. vol. 



for the year 1861, p. 72, 1863. 



— — Dumortier. Depots Jurass. du Bassin du Rhone, p. 132, 



pi. xxiv, fig. 1, 1867. 



— halecis, Buckman. Murchison's Geol. of Cheltenham, p. 104, 



pi. xi, fig. 9, 1845. 

 Arietites spinabies, Tate Sf Blake. Yorkshire Lias, p. 286, 1876. 



— Sauzeanus, Tate §• Blake. Ibid., p. 288, 1876. 



Diagnosis. — Shell compressed, whorls quadrate, one third involute, ornamented 

 with twenty costae ; the ribs are slightly bent, the convexity obliquely backwards, and they 

 terminate in a tubercle at the outer margin of the siphonal area, which is flat, with a 

 slightly elevated central ridge. 



Dimensions. — The large specimen, transverse diameter 205 millimetres, height of 

 aperture 67 millimetres, width of aperture 68 millimetres. 



Description. — This remarkable Ammonite has an extremely quadrate physiognomy, the 

 whorls, about one third involute, are square and ornamented in the large specimen figured 

 with twenty ribs, which are simple, slightly bent with their convexity obliquely backwards, 

 and they terminate at the angle of the margin in small well-marked tubercles (PI. VIII, figs. 

 1, 2, 4). The siphonal area is large and quadrate, and a considerable eminence rises in the 

 middle line, which, however, does not form a keel, nor are there any traces of lateral sulci 

 as in the true keeled Arietites. The spire, formed of square-shaped whorls, imparts a 



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